JP4145265B2 - Infrared receiver - Google Patents

Description

  The present invention relates to an infrared receiver that receives a high-frequency signal transmitted using infrared as a medium, and more particularly to an infrared receiver that receives a plurality of high-frequency signals having different reference frequencies, for example.

  As this type of infrared receiving apparatus, there is one conventionally applied to a wireless microphone system disclosed in Non-Patent Document 1, for example. According to this prior art, as shown in FIG. 25, one or more (up to four) light receiving sensors 1 as infrared receivers are attached to a ceiling or a wall surface, for example. Each light receiving sensor 1 is connected to a sensor coupler 3 via a coaxial cable 2, and the sensor coupler 3 is connected to an optical wireless tuner 5 via another coaxial cable 4. On the other hand, for example, a hand-type optical wireless microphone 6 is prepared on the transmission side. Although not shown in the drawing, in addition to the hand type, a tie pin type optical wireless microphone is also prepared.

  In this configuration, when an utterance is made using the optical wireless microphone 6, an FM (Frequency Modulation) signal including the content of the utterance is generated in the optical wireless microphone 6. The FM signal is further converted into infrared rays (luminance modulation) and emitted from the optical wireless microphone 6. The emitted infrared light is incident on the light receiving sensor 1 in an appropriate place, for example, in the vicinity of the optical wireless microphone 6. The light receiving sensor 1 converts incident infrared rays into an electric signal, and further performs a tuning process on the electric signal. Thereby, the FM signal is reproduced. The reproduced FM signal is input from the light receiving sensor 1 to the optical wireless tuner 5 through the coaxial cable 2, the sensor coupler 3 and the coaxial cable 4. The optical wireless tuner 5 performs demodulation processing on the input FM signal and extracts an audio signal. The extracted audio signal is input to a speaker (not shown) through an amplifier or a mixer (not shown), thereby reproducing the above-described speech content.

This conventional technology complies with the standard related to the infrared spatial analog audio transmission system called “CPX-1206” established by the Japan Electronics Opportunity Industry Association (EIAJ), and can simultaneously connect up to four optical wireless microphones 6 at the same time. It can be used, i.e. it has four channels. Specifically, four channels of 1ch to 4ch (H1 to H4 in the CPX-1206 standard) are prepared, and the optical wireless microphone 6 is dedicated for each channel (model: WM-PH711, WM). -PH712, WM-PH713 and WM-PH714) are prepared. On the other hand, as the light receiving sensor 1, a dedicated one for 1ch and 2ch (model: WT-PS31) and a dedicated one for 3ch and 4ch (model: WT-PS32) are prepared. As for the optical wireless tuner 5, a dedicated one for 1ch and 2ch (model: WT-PH31) and a dedicated one for 3ch and 4ch (model: WT-PH32) are prepared. Therefore, the optical wireless microphone 6, the light receiving sensor 1, and the optical wireless tuner 5 are provided with all types (models), thereby enabling simultaneous communication using a total of four channels from 1ch to 4ch.
Victor Company of Japan “Optical Wireless Microphone System WT-PH31 Series” catalog, [online], [Search April 7, 2004], Internet <URL; http://www.jvc-victor.co.jp/ pdf / pro / catalog / WT-PH31.pdf>

  As described above, in the prior art, two channels of 1ch and 2ch, or 3ch and 4ch can be simultaneously received by one light receiving sensor 1, but in order to realize this, in the tuning process described above, so-called Q (Quality factor) Dump processing is performed. That is, by deliberately lowering the Q value of the tuning circuit responsible for the tuning process, the characteristics (selectivity) near the tuning frequency are flattened to widen the reception bandwidth. However, when the Q dump process is performed, the reception sensitivity naturally decreases in the vicinity of the tuning frequency and in the surrounding area. As a result, there arises a problem that the infrared light receivable range (communication possible range) by each light receiving sensor 1 is narrowed.

  In addition, although the reception bandwidth is widened by such Q dump processing, the conventional technology can receive only two channels simultaneously by one light receiving sensor 1. Accordingly, in order to simultaneously receive three or more channels, two types of light receiving sensor 1 (and optical wireless tuner 5) are required as described above, and accordingly, the configuration of the entire system becomes larger, and There is a problem of high costs.

  Accordingly, an object of the present invention is to provide an infrared receiver having a higher sensitivity and a wider reception bandwidth than in the past in order to solve these problems.

In a first aspect of the present invention, there is provided an infrared receiver for simultaneously receiving one or more high-frequency signals having different reference frequencies transmitted using infrared as a medium, and a light receiving means for receiving the infrared and converting it into an electrical signal, Characteristic control means including a tuning means for receiving the electrical signal converted by the light receiving means and performing a tuning process on the electrical signal, and a changeover switch that can be manually switched to change the frequency characteristic of the tuning means in accordance with the operation of the changeover switch. And. Here, the tuning means has a tuning frequency between the lowest reference frequency and the highest reference frequency. The characteristic control means, changing the Q value of the frequency characteristic of the tuning means, is characterized in.

In the first invention, the infrared rays transmitted from the transmission side are received by the light receiving means and converted into electrical signals. Then, the converted electric signal is input to the tuning means, where tuning processing is performed. The frequency characteristic of the tuning means is controlled by a characteristic control means including a changeover switch that can be manually switched . Specifically, when the changeover switch is switched, the Q value of the frequency characteristic of the tuning means changes, and so-called Q dump processing is performed.

Incidentally, as the number of high-frequency signal is small to be received, i.e. as actually the number of the infrared transmission device is less used, to increase the Q value, the greater the number of high-frequency signal to be received, that is actually As the number of infrared transmitters used increases, the Q value may be reduced .

Then, the light receiving means comprises a photodiode infrared rays are incident, the tuning means may as including a capacitive component of the photodiode component. That is, the photodiode is a so-called capacitive element having a junction capacitance. Therefore, a tuning means is constructed using the capacitance component of the photodiode, and more specifically, a parallel resonant circuit is constructed. In this way, the tuning means can be realized easily and inexpensively.

According to a second aspect of the present invention, there is provided an infrared receiving apparatus that simultaneously receives one or more high-frequency signals having different reference frequencies that are transmitted using infrared rays as a medium, and a plurality of light-receiving units that receive the infrared rays and convert them into electrical signals. , separate a plurality of tuning means electrical signal converted by the light receiving means corresponding respectively provided corresponding to each light-receiving means is to perform the tuning process in the electric signal is input, a plurality of tuning means manually And an combining means for combining the output signals of the tuning means enabled by the enabling means. Here, each tuning means has tuning frequencies at different frequencies in the first frequency band from the lowest reference frequency to the highest reference frequency. Then, when two of the tuning means adjacent to each other in the tuning frequency are activated by the enabling means, synthesis is performed at each frequency in the second frequency band from one of the two adjacent tuning frequencies to the other. The frequency characteristics of the respective tuning means are set so that the output level of the means is equal to or higher than a predetermined level and one or more reference frequencies exist in the second frequency band. Furthermore, the number of tuning means is smaller than the number of infrared transmission devices on the infrared transmission side .

That is, in the second invention, infrared rays transmitted from the transmission side are received by a plurality of light receiving means and converted into electrical signals. Then, each converted electric signal is input to the corresponding tuning means, where it is subjected to tuning processing. However, these tuning means is manually are individually enabled by Enabling means. Only the output signal of the activated tuning means is synthesized by the synthesis means. Therefore, a signal that combines the tuning results of the validated tuning means is output from the synthesizing means. Here, each tuning means has tuning frequencies at different frequencies in the first frequency band from the lowest reference frequency to the highest reference frequency. Then, when two of the tuning means adjacent to each other in the tuning frequency are activated by the enabling means, the synthesizing means in each frequency in the second frequency band from one of the two adjacent tuning frequencies to the other. as the output level becomes a predetermined level or higher, so details will be a level sufficient to receive a high frequency signal to be received with good sensitivity, and one or more reference frequency to the second frequency band The frequency characteristics of the respective tuning means are set so as to exist. Further, the number of tuning means is smaller than the number of infrared transmission devices on the infrared transmission side.

In the second aspect of the invention , each of the light receiving means includes a photodiode to which infrared rays are incident, and each of the tuning means may include a capacitance component of the photodiode of the corresponding light receiving means as a component. Good.

According to the first aspect of the invention , the frequency characteristic of the tuning means is controlled so that the high frequency signal can be received with good sensitivity according to the number of high frequency signals to be received. On the other hand, in the above-described conventional technology, a constant Q dump process is always performed regardless of the number of channels to be received (the number of optical wireless microphones 6 to be used). The Q dump process is always performed even in a situation where the process need not be performed. Therefore, unlike such prior art, a high frequency signal to be actually received can always be received with an optimum sensitivity.

According to the second invention , a plurality of tuning means are provided, and the plurality of tuning means are individually activated according to the number of high-frequency signals to be received. Then, the frequency characteristics of each tuning unit are set so that the overall tuning level by the activated tuning unit is a level sufficient to receive the high-frequency signal to be received with good sensitivity. Therefore, it is possible to realize an infrared receiver having high sensitivity and a wide reception bandwidth as compared with the above-described conventional technique in which Q dump processing is performed in order to simultaneously receive two channels.

A first reference example of the present invention will be described with reference to FIGS.

In the first reference example , the present invention is applied to an infrared conference system 10 as shown in FIG. 1, and the infrared conference system 10 includes one center device 12 as a main device and a relay device. , And a plurality of terminal devices 18, 18,... Each having a microphone 16. Among these, the center apparatus 12 is installed in the corner of a meeting room, for example, and each light transmission / reception apparatus 14,14, ... is attached to the ceiling or wall surface of the meeting room. And each terminal device 18, 18, ... is arrange | positioned at the appropriate position of the conference room, for example, on the table for each speaker. Each terminal device 18, 18,... Is assigned an individual identification number.

  The center device 12 has a plurality of, for example, four input / output terminals 20, 20,..., And one or more light transmitting / receiving devices 14 are connected to each of the four input / output terminals 20, 20,. be able to. Specifically, for example, like the input / output terminal 20 shown at the top in FIG. 1, one transmitter / receiver 14 can be connected through one coaxial cable 22 as a transmission line. . Further, like the input / output terminal 20 shown second from the top in FIG. 1, a single mixer / distributor 24 is used, so that a plurality of transmitters / receivers 14, 14,. Can be connected. Further, by using a plurality of (two in FIG. 1) mixing / distributing units 24, 24,... Like the input / output terminal 20 shown third from the top in FIG. ) Transmitter / receiver devices 14, 14,... Can also be connected. And there may exist what is called a vacant terminal to which the transmission / reception apparatus 14 is not connected like the input / output terminal 20 shown at the bottom in FIG.

  The mixer / distributor 24 includes one primary terminal 26 and four secondary terminals 28, 28,..., And signals input from the primary terminal 26 are input to the secondary terminals 28, 28,. .., Or signals input from the secondary terminals 28, 28,... Are mixed and output from the primary terminal 26. For this reason, the primary terminal 26 is connected to the input / output terminal 20 of the center device 12 via the coaxial cable 22 or to the secondary terminal 28 of another mixing / distributing device 24. Each secondary terminal 28 is connected to the light transmitting / receiving device 14 via the coaxial cable 22 or to the primary terminal 26 of another mixing / distributing device 24. Further, the secondary terminal 28 may be an empty terminal. Further, as will be described later, the coaxial cable 22 is overlaid with direct current power used as a drive power source for each of the light transmitting / receiving devices 14, 14,... To the secondary terminals 28, 28,... The mixing / distributing device 24 is installed, for example, on the ceiling or behind the wall.

  Here, the overall operation of the infrared conference system 10 will be briefly described. For example, it is assumed that a request for speech is made by a certain terminal device 18 now. This speech request is made by operating a speech request switch on an operation panel (not shown) provided in the terminal device 18. Then, in the terminal device 18, uplink control data indicating that a speech request has been made is generated. In this uplink control data, an identification number indicating the request source of the message request is also incorporated. Then, this uplink control data is converted (frequency modulation) into an uplink FM signal having a predetermined reference frequency, and further, this uplink FM signal is converted into an infrared ray having a wavelength of 870 [nm] (luminance modulation), Fired from the terminal device 18. In order to emit this infrared ray, the terminal device 18 includes an infrared light emitting diode (not shown).

  Ascending infrared rays emitted from the terminal device 18 are incident on an appropriate place, for example, the light transmitting / receiving device 14 in the vicinity of the terminal device 18. The light transmitting / receiving device 14 converts the incident infrared light into an electrical signal, and further performs a tuning process on the electrical signal. As a result, the above-described uplink FM signal is extracted. The extracted upstream FM signal is sent to the center device 12 via the coaxial cable 22 or in addition to one or more mixing / distributing devices 24.

  The center device 12 receives the uplink FM signal sent from the light transmitting / receiving device 14 and performs demodulation processing on the received uplink FM signal. Thereby, the uplink control data is reproduced. Furthermore, the center device 12 analyzes the reproduced uplink control data, and recognizes that the speech request has been made this time and the terminal device 18 that is the request source of the speech request. Then, downlink control data indicating that the terminal device 18 is permitted to speak is generated, and the downlink control data is converted into a downlink FM signal having a reference frequency different from that of the above-described uplink FM signal. This downstream FM signal is sent to all the light transmitting / receiving devices 14, 14,... Via the coaxial cable 22 or in addition to one or more mixing / distributing devices 24.

  Each of the light transmitting / receiving devices 14, 14,... Includes an infrared light emitting diode (not shown), and causes the infrared light emitting diode to emit light in accordance with a downstream FM signal sent from the center device 12. Thereby, infrared rays having a wavelength of 870 [nm] are emitted from each of the light transmitting / receiving devices 14, 14,... (Infrared light emitting diodes).

  The downstream infrared rays emitted from the light transmitting / receiving devices 14, 14,... Are appropriately incident on the terminal devices 18, 18,. Each terminal device 18 converts incident infrared rays into an electrical signal, and performs a tuning process on the converted electrical signal. As a result, the downlink FM signal is extracted. Further, the terminal device 18 performs demodulation processing on the extracted downlink FM signal to reproduce downlink control data. Then, it is determined whether or not the reproduced downlink control data is sent to itself, for example, whether or not its own identification number is incorporated in the downlink control data. Here, only the terminal device 18 that has received the downlink control data sent to itself is allowed to speak and is thus validated.

  When a speech is made by the activated terminal device 18, that is, when sound is input to the microphone 16 of the terminal device 18, an uplink FM signal is generated again based on the sound signal output from the microphone 16. Is done. Note that the reference frequency of this uplink FM signal is specified by downlink control data. Then, the generated uplink FM signal is converted into infrared rays and emitted from the terminal device 18 in the same manner as described above.

  Ascending infrared rays emitted from the terminal device 18 are incident on the light transmitting / receiving device 14 in the vicinity of the terminal device 18 as described above. The light transmitting / receiving device 14 converts the incident infrared light into an electrical signal, and further performs a tuning process on the electrical signal. Thereby, an uplink FM signal is extracted. Then, the extracted uplink FM signal is transmitted to the center device 12.

  The center device 12 receives the uplink FM signal sent from the light transmitting / receiving device 14 and performs demodulation processing on the received uplink FM signal. As a result, an audio signal according to the above-mentioned speech is reproduced. The reproduced audio signal is supplied to an external speaker (not shown) connected to an external output terminal (not shown) of the center device 12. Thereby, the voice representing the content of the utterance is reproduced. Furthermore, the center device 12 generates a downlink FM signal again based on the reproduced audio signal. This downstream FM signal is sent to each of the light transmitting / receiving devices 14, 14,.

  Each of the light transmitting / receiving devices 14, 14,... Causes the above-described infrared light emitting diodes to emit light according to the supply of the downstream FM signal transmitted from the center device 12. As a result, infrared rays are emitted from the respective light transmitting / receiving devices 14, 14,... (Infrared light emitting diodes), and the infrared rays are incident on the terminal devices 18, 18,.

  Each of the light transmitting / receiving devices 14, 14,... Converts incident infrared rays into electric signals, and performs a tuning process on the converted electric signals. As a result, the downlink FM signal is extracted. Further, the terminal device 18 performs demodulation processing on the extracted downlink FM signal to reproduce the audio signal. This audio signal is input to a monitor speaker (not shown) provided on the above-described operation panel. As a result, a sound representing the above-mentioned speech content is reproduced. That is, the voice can be monitored in each terminal device 18.

By the way, in the first reference example , a maximum of four terminal devices 18, 18,. In other words, four channels are prepared as uplink audio channels from the terminal devices 18, 18,... To the center device 12 through the light transmitting / receiving devices 14, 14,. Specifically, as shown in FIG. 2, four channels CH1, CH2, CH3, and CH4 are prepared as uplink audio channels, and each reference frequency (carrier frequency) is 7.35 [MHz. ], 8.10 [MHz], 8.55 [MHz], and 9.15 [MHz]. In addition to these four uplink voice channels CH1, CH2, CH3 and CH4, a control channel CH0 dedicated to uplink control data is also prepared. The reference frequency of the control channel CH0 is 6.45 [MHz].

  On the other hand, two channels are prepared as downlink channels from the center device 12 to the terminal devices 18, 18,... Via the light transmitting / receiving devices 14, 14,. Specifically, as shown in FIG. 2, a channel CH1 having a reference frequency of 1.95 [MHz] and a channel CH2 having a reference frequency of 2.25 [MHz] are prepared. Of these, the channel CH1 is a channel for main audio, and the channel CH2 is a channel for sub audio. Normally, the main audio channel CH1 is preferentially used, and the sub audio channel CH2 is used, for example, when broadcasting simultaneous interpretation sounds. This simultaneous interpretation sound is input from, for example, an external microphone (not shown) connected to an external input terminal (not shown) of the center device 12. Further, the above-described operation panel of each terminal device 18, 18,... Is provided with a channel selection switch (not shown) for arbitrarily selecting one of the main audio channel CH1 and the sub audio channel CH2. Only the sound of the channel CH1 or CH2 selected by the channel selection switch (the contents of speech or the simultaneous interpretation sound) is reproduced on the terminal devices 18, 18,.

  Each of the downlink channels CH1 and CH2 is also used as a control channel for transmitting downlink control data. Specifically, the downlink control data is transmitted via the downlink channel CH1 or CH2 while being mixed with the downlink audio signal. At this time, the downlink control data is superimposed on the audio signal by a subcarrier signal (subcarrier) having a frequency of 30 [kHz], and, for example, an FSK (Frequency Shift Keying) method is adopted as the modulation method of the downlink control data. The Note that the control data transmitted through these downlink channels CH1 and CH2 may be the same or different from each other.

Thus, in the first reference example , five uplink channels CH0 to CH4 and two downlink channels CH1 and CH2 are prepared. Each of the downlink channels CH1 and CH2 is also used as an audio channel and a control channel. In order to realize this, each of the center device 12, the light transmitting / receiving devices 14, 14,... And the terminal devices 18, 18,.

  Specifically, as shown in FIG. 3, the center device 12 has the four input / output terminals 20, 20,... Described above, and each of the four input / output terminals 20, 20,. An upstream FM signal is input from the (transmission / reception device 14). The uplink FM signal is input to an RF (Radio Frequency) mixing / distributing circuit 122 via DC cut capacitors 120, 120,... Provided for each input / output terminal 20. The RF mixing / distributing circuit 122 mixes (up to) four FM signals input via the capacitors 120, 120,..., And the mixed uplink FM signal is output from the RF mixing / distributing circuit 122. The signal is input to the receiving circuit 126 through the high pass filter 124.

  Although not shown in the figure, the reception circuit 126 has five demodulation circuits corresponding to the respective uplink channels CH0 to CH4, and (mixed) uplink FM signals are input to each of these five demodulation circuits. Is done. Each demodulation circuit performs demodulation processing on the input uplink FM signal and extracts signals of different uplink channels CH0 to CH4. As a result, the uplink control data of the control channel CH0 and the audio signals of the uplink audio channels CH1 to CH4 are reproduced. The reproduced control data is input to the control circuit 128, and each audio signal is input to an AF (Audio Frequency) mixing / distributing circuit 130.

The control circuit 128 includes a CPU (Central
Processing Unit), and the uplink control data input from the receiving circuit 126 is analyzed. Then, based on the analysis result, downlink control data is generated and input to the transmission circuit 132. Further, an operation key (not shown) as an operation means is connected to the control circuit 128, and the control circuit 128 controls the operation of the AF mixing / distributing circuit 130 described below according to the operation of the operation key. Generate a control signal.

  The AF mixing / distributing circuit 130 mixes, for example, the audio signal input from the receiving circuit 130 in accordance with the control signal described above. Then, the mixed audio signal is sent out to the external output terminal described above, and is input to the transmission circuit 132 as a down audio signal of the main audio channel CH1. In addition, an audio signal (for example, simultaneous interpretation sound) is input to the AF mixing / distributing circuit 130 via the external input terminal described above. In the AF mixing / distributing circuit diagram 130, the audio signal input through the external input terminal is input to the transmission circuit 132 as, for example, a downstream audio signal of the sub audio channel CH2.

  As shown in FIG. 4, the transmission circuit 132 includes two FM signal generation circuits 200 and 200a. One of these, for example, the FM signal generation circuit 200 shown on the upper side in FIG. 4 is a circuit for the main audio channel CH1, and the downstream audio signal of the main audio channel CH1 is input from the AF mixing / distributing circuit 130. The AF amplifier circuit 202 is provided. The downstream audio signal input to the AF amplifier circuit 202 is amplified here and then input to a superimposing circuit 204 as a mixing unit. Further, the FM signal generation circuit 200 includes a data modulation circuit 206 to which downlink control data is input from the control circuit 128. The data modulation circuit 206 also receives a subcarrier signal having a frequency of 30 [kHz] from the sub-local oscillation circuit 208, and the data modulation circuit 206 performs frequency modulation (FSK) on the subcarrier signal using downlink control data. ) The so-called subcarrier signal after the frequency modulation is also input to the superimposing circuit 204.

  Superimposition circuit 204 superimposes the subcarrier signal input from data modulation circuit 206 on the downlink audio signal input from AF amplification circuit 202. Then, the downlink audio signal on which the subcarrier signal is superimposed, that is, the mixed signal is further input to the modulation circuit 210. The modulation circuit 210 also receives a carrier signal having a frequency of 1.95 [MHz] from the main local oscillation circuit 212, and the modulation circuit 210 performs frequency modulation (FM) on the carrier signal using a mixed signal. Thereby, a downlink FM signal is generated, and the generated downlink FM signal is amplified by the RF amplifier circuit 214 and then input to the mixing circuit 216.

  In contrast to the FM signal generation circuit 200 for the main audio channel CH1 configured as described above, the FM signal generation circuit 200a for the sub audio channel CH2 is also an AF amplification circuit similar to the FM signal generation circuit 200 for the main audio channel CH1. 202a, a superimposing circuit 204a, a data modulation circuit 206a, a sub local oscillation circuit 208a, a modulation circuit 210a, a main local oscillation circuit 212a, and an RF amplifier circuit 214a. However, the frequency of the carrier signal input from the main local oscillation circuit 212a to the modulation circuit 210a is 2.25 [MHz]. The downlink FM signal generated by the FM signal generation circuit 200a for the sub audio channel CH2 is also input to the mixing circuit 216.

  The mixing circuit 216 mixes two downlink FM signals input from the FM signal generation circuits 200 and 200a. The mixed downlink FM signal is used as the output signal of the transmission circuit 132.

  Returning to FIG. 3, the downlink FM signal output from the transmission circuit 132 is input to the RF mixing / distributing circuit 122 via the low-pass filter 134. Note that the cut-off frequency of the low-pass filter 134 is higher than the upper limit frequencies of the downstream channels CH1 and CH2 (a frequency obtained by adding a predetermined bandwidth to 2.25 [MHz]), and the lower limit frequencies of the upstream channels CH0 to CH4. The value is lower than (a frequency obtained by adding a predetermined bandwidth to 6.45 [MHz]), for example, 2.70 [MHz]. On the other hand, the cutoff frequency of the high-pass filter 124 described above is higher than the cutoff frequency of the low-pass filter 134 and lower than the lower limit frequency of the upstream channels CH0 to CH4. For example, 5.16 [MHz] It is said that. Therefore, the downlink FM signal output from the low-pass filter 134 is not input to the receiving circuit 126 via the high-pass filter 124. Further, the above-described uplink FM signal output from the RF mixing / distributing circuit 122 is not input to the transmission circuit 132 via the low-pass filter 134.

  The RF mixing / distributing circuit 122 distributes the downlink FM signal input from the low-pass filter 134 into four. The distributed downlink FM signal is sent to each input / output terminal 20, 20,... Via each capacitor 120, 120,..., And externally (transmission / reception device 14) from each input / output terminal 20, 20,. Is output.

  Further, the center device 12 has a power supply circuit 136 that generates DC power of, for example, +24 [V] as a drive power supply for each of the light transmitting / receiving devices 14, 14,. The DC power is supplied to the input / output terminals 20, 20,... Via the individual AC cut low-pass filters 138, 138,. Then, the signals are output to the outside from the input / output terminals 22, 22,.

  On the other hand, as shown in FIG. 5, each light transmitting / receiving device 14 includes a terminal 140 to which the coaxial cable 22 is connected. That is, a downlink FM signal and DC power are input from the outside (center device 12) via the terminal 140, and an uplink FM signal is output to the outside.

  Among these, the DC power input from the outside via the terminal 140 is input to the power supply circuit 144 through the AC cut low-pass filter 142. The power supply circuit 144 generates a plurality of types (voltage values) of DC power supply voltages Vcc for driving each circuit in the light transmitting / receiving device 14 based on the input DC power.

  The downstream FM signal is input to the low pass filter 148 and the high pass filter 150 via the DC cut capacitor 146. Here, the cutoff frequency of the low-pass filter 148 is set to a value higher than the upper limit frequencies of the downlink channels CH1 and CH2 and lower than the lower limit frequency of the uplink channels CH0 to CH4, for example, 2.70 [MHz]. Has been. On the other hand, the cutoff frequency of the high pass filter 150 is higher than the cutoff frequency of the low pass filter 148 and lower than the lower limit frequency of the upstream channels CH0 to CH4. For example, 5.16 [MHz] It is said that. Therefore, the downstream FM signal input to the low pass filter 148 passes through the low pass filter 148 and is input to the RF amplifier circuit 152. On the other hand, the downlink FM signal input to the high pass filter 150 does not pass through the high pass filter 150.

  The downlink FM signal input to the RF amplifier circuit 152 is amplified here and then input to the light transmission circuit 154. The light transmission circuit 154 includes the above-described infrared light emitting diode as a light emitting unit, and causes the infrared light emitting diode to emit light according to the downstream FM signal input from the RF amplification circuit 152. Thereby, infrared rays are emitted from the infrared light emitting diodes. A plurality of infrared light emitting diodes are provided, and the plurality of infrared light emitting diodes are arranged in different directions. Thereby, infrared rays are emitted in different directions, and a wide communication (transmission) area is secured.

  The light transmitting / receiving device 14 also includes a light receiving circuit 156. The light receiving circuit 156 receives upstream infrared rays transmitted from the terminal devices 18, 18,... And converts them into electrical signals, and performs tuning processing on the electrical signals to extract upstream FM signals. The extracted uplink FM signal is amplified by the RF amplifier circuit 158, then sent to the terminal 140 via the high-pass filter 150 and the capacitor 148, and output from the terminal 140 to the outside (center device 12).

  The upstream FM signal output from the high pass filter 150 is also input to the low pass filter 148. As described above, the cutoff frequency of the low pass filter 148 is lower than the lower limit frequency of the upstream channels CH0 to CH4. Value. Therefore, the upstream FM signal input to the low-pass filter 148 does not pass through the low-pass filter 148 and is input to the downstream RF amplification circuit 152.

  Now, the light receiving circuit 156 needs to simultaneously receive the five upstream channels CH0 to CH4. That is, it is necessary to guarantee a reception band of 6.45 [MHz] to 9.15 [MHz] (strictly, a slightly wider band than this). For this reason, the light receiving circuit 156 is configured as shown in FIG.

  In other words, the light receiving circuit 156 includes two photoelectric conversion circuits 220 and 220a. One of these, for example, the photoelectric conversion circuit 220 shown on the upper side in FIG. 6 has a plurality of, for example, four photodiodes 222 as light receiving means. These photodiodes 222, 222,... Are connected in parallel to each other, and a DC power supply voltage Vcc is applied to each cathode terminal. The anode terminals of the photodiodes 222, 222,... Are connected to the ground potential (GND) via the coil 224. That is, a so-called reverse bias voltage is applied to each photodiode 222, 222,.

  According to this configuration, when the upstream infrared light is incident on the photodiodes 222, 222,..., The voltage at the anode terminal of the photodiodes 222, 222,. Here, since the photodiodes 222, 222,... Have a capacitance component including a junction capacitance, a parallel resonance circuit, that is, a tuning circuit 226 is formed by the capacitance component and the inductance of the coil 224. The tuning frequency (resonance frequency) f1 of the tuning circuit 226 is determined by the magnitude of the capacitance component and the inductance value of the coil 224. Of these, the magnitude of the capacitance component is determined by the number of photodiodes 222, 222,..., And the tuning frequency f 1 is adjusted by the inductance value of the coil 224. This tuning frequency f1 is set to a value lower than the center frequency (7.80 [MHz]) of the required reception band (6.45 [MHz] to 9.15 [MHz]), for example. Is set between the reference frequencies (6.45 [MHz] and 7.35 [MHz]) of the uplink channels CH0 and CH1, more specifically, the reference frequency (7.35 [MHz]) of the downlink channel CH1. It is about 7.2 [MHz] which is a little lower than that. As a result, among the electrical signals converted by the photodiodes 222, 222,..., A signal in a frequency band near about 7.2 [MHz] is extracted by the tuning circuit 226.

  The signal extracted by the tuning circuit 226 is input to the preamplifier circuit 230 via the coupling capacitor 228, and more specifically, an N-channel FET (Field Effect) constituting the preamplifier circuit 230. Transistor) 232 is input to the gate terminal. The preamplifier circuit 230 includes an FET 232, a bias resistor 234 connected between the gate terminal of the FET 232 and the ground potential, and a power supply connected between the drain terminal of the FET 232 and the power supply line (Vcc). Resistor 236, a source grounding resistor 238 connected between the source terminal of the FET 232 and the ground potential, and a bypass capacitor 240 connected in parallel with the resistor 238. . Further, in the vicinity of the preamplifier circuit 230, the power supply line is connected to the ground potential via a bypass capacitor 242.

  The signal amplified by the preamplifier circuit 230 is input to an adder circuit 246 as a synthesizing unit via a DC cut capacitor 244, and in detail, via an input resistor 248 that constitutes the adder circuit 246. Are input to the inverting input terminal of the operational amplifier 250. The inverting input terminal of the operational amplifier 250 is connected to the output terminal of the operational amplifier 250 via the feedback resistor 252 and the non-inverting input terminal is connected to the ground potential.

  In contrast to the photoelectric conversion circuit 220 having such a configuration, the other photoelectric conversion circuit 220a also has four photodiodes 222a, 222a,..., A coil 224a, a coupling capacitor 228a, a preamplifier similar to the photoelectric conversion circuit 220. A circuit 230a (FET 232a, resistors 234a, 236a, 238a, and a capacitor 240a), a bypass capacitor 242a, and a DC cut capacitor 244a are provided. However, the coil 224a has an inductance value different from that of the coil 224. More specifically, the reference frequencies (8.55 [8.55 [8.5 [ More specifically, the value is about 8.7 [MHz] slightly lower than the reference frequency (9.15 [MHz]) of the downlink channel CH4 so that the value is between [MHz] and 9.15 [MHz]). Thus, the inductance value of the coil 224a is selected. The output signal of the photoelectric conversion circuit 220a is also input to the adder circuit 246, and more specifically, input to the inverting input terminal of the operational amplifier 250 via the input resistor 246a.

  The adder circuit 246 adds the signals input from the photoelectric conversion circuits 220 and 220a, and outputs the addition result. That is, the summing circuit 246 outputs a signal that combines the reception results of the two photoelectric conversion circuits 220 and 220a, in other words, the tuning results of the two tuning circuits 226 and 226a. Then, the output signal of the adder circuit 246 (the operational amplifier 250) is input as an output signal of the light receiving circuit 156 to the RF amplifier circuit 158 in FIG.

  FIG. 7 shows frequency characteristics of the light receiving circuit 156. Specifically, a curve A indicated by a solid line in FIG. 7 represents a result of measuring the output signal of the light receiving circuit 156 with a spectrum analyzer. A curve B indicated by a dotted line in FIG. 7 is for reference, and represents a result of measuring an output signal of a so-called conventional infrared light receiving circuit having only one tuning circuit under the same conditions. The tuning frequency of the reference light receiving circuit is 7.8 [MHz] (center frequency of 6.45 [MHz] to 9.15 [MHz]). In addition, the signal level value indicated on the vertical axis in FIG. 7 represents a relative value based on the maximum value of the signal level of the curve B as a reference (0 [dB]).

  As can be seen from FIG. 7, according to the light receiving circuit 156 having the characteristic of the curve A, the same frequencies (6.45 [MHz], 7.35 [MHz], 8.10 [MHz] as the uplink channels CH0 to CH4. ], 8.55 [MHz] and 9.15 [MHz]) at about -6.4 [dB], -2.9 [dB], -6.8 [dB], and -4.3 [dB], respectively. ] And −5.4 [dB] signal levels (selectivity) are obtained. In other words, such a signal level is obtained by setting the tuning frequencies f1 and f2 of the tuning circuits 226 and 226a as described above (to frequencies of about 7.2 [MHz] and about 8.2 [MHz]). be able to. On the other hand, according to a conventional light receiving circuit having the characteristic of curve B, a signal substantially equal to or higher than that of the light receiving circuit 156 at a frequency close to the tuning frequency, for example, the same frequency as the upstream channels CH1 to CH3. Although a level is obtained, the signal level is very small (about 3 [dB]) compared to the light receiving circuit 156 at a frequency away from the tuning frequency, for example, the same frequency as the upstream channels CH0 and CH4.

Here, for example, if it is assumed that a signal level of −8 [dB] or higher is necessary to obtain good reception sensitivity in each of the upstream channels CH0 to CH4, according to the light receiving circuit 156 in this first reference example . This condition is satisfied in all the upstream channels CH0 to CH4. That is, good sensitivity can be obtained in all the upstream channels CH0 to CH4. On the other hand, according to the conventional light receiving circuit so far, the condition is not satisfied in the two upstream channels CH0 and CH4, that is, good sensitivity cannot be obtained in the two upstream channels CH0 and CH4. Note that even if such a conventional light receiving circuit is subjected to Q dump processing as in the prior art described above, for example, only the vicinity of the peak of the curve B in FIG. 7 is flattened, and the signal level is further increased. descend. That is, according to the light receiving circuit 156 in the first reference example, it is possible to obtain a wider reception bandwidth than the conventional one while ensuring high reception sensitivity.

  Note that the photodiode 222 that constitutes the low-frequency photoelectric conversion circuit 220 in FIG. 6 is externally as shown in FIG. That is, it has a flat rectangular parallelepiped main body 260, and a rectangular light receiving surface 262 is formed on one main surface (upper surface in FIG. 6) side of the main body 260. A plurality of lead terminals 264, 264,... Are provided on the other main surface side of the main body 260. The photodiode 222 has a normal line passing through the center of the light receiving surface 222b as a light receiving central axis (optical axis), and the light receiving central axis is a reference (incident angle is 0 degree) as shown in FIG. 8B. It has a generally circular directional characteristic. Specifically, if a region (angle) having a relative sensitivity of half value (0.5) or more is valid, the effective field of view is about ± 65 degrees around the light receiving central axis. On the other hand, the photodiode 222a of the high-frequency photoelectric conversion circuit 220a is also of the same standard, and has the same main body 260a, light receiving surface 262a, and lead terminals 264a, 264,.

  These eight photodiodes 222, 222,... And 222a, 222a,..., With their respective light receiving surfaces 262, 262,... And 262a, 262a,. It is arranged to draw a circle (octagon). Further, low-frequency photodiodes 222, 222,... And high-frequency photodiodes 222a, 222a,... Are alternately arranged along the circle. In other words, the low-frequency photodiodes 222, 220,... Are arranged with their respective light receiving surfaces 262, 262,... Oriented 90 degrees in different directions, and the photodiode 222a of the high-frequency photoelectric conversion circuit 220a. , 220a,... Are also arranged with their light receiving surfaces 262a, 262a,. With this arrangement, the light receiving circuit 156 can receive the upstream channels CH0 to CH4 evenly in space.

  That is, when the directivity characteristics of the photodiodes 222, 222,... And 222a, 222a,. For example, when attention is paid to the low-frequency photodiodes 222, 222,..., As shown by dotted lines 270, 270,... In FIG. Is done. Then, when these receivable areas 270, 270,... Are combined, a receivable area generally indicated by a dotted line 272 in FIG. In other words, since the four receivable areas 270, 270,... By the respective photodiodes 222, 222,... Are spatially interpolated (covered), a receivable area of 360 degrees as shown by the dotted line 272 is formed. The Similarly, in FIG. 10, when attention is paid to the high-frequency photodiodes 222a, 222a,..., As shown by alternate long and short dash lines 270a, 270a,. A possible area is formed. Then, when these receivable areas 270a, 270a,... Are combined, a receivable area of approximately 360 degrees as shown by a one-dot chain line 272a in FIG. As described above, the receivable areas 272 and 272a extending 360 degrees are formed in each of the low frequency band and the high frequency band, so that signals (infrared rays) of the upstream channels CH0 to CH4 transmitted from various directions can be received evenly. it can.

  9 to 11 are views of the photodiodes 222, 222,... And 222a, 222a,... Of the light transmitting / receiving device 14 in a state where they are attached to the ceiling, for example, as viewed from above (the back side of the ceiling). is there. 9 to 10, for convenience of explanation, each of the photodiodes 222, 222,... And 222 a, 222 a,... Has a light receiving surface 262, 262,. However, the light receiving surfaces 262, 262,... And 262a, 262a,... Are actually attached in a state of facing obliquely downward (slightly on the floor surface side).

  Next, the terminal device 18 will be described. As shown in FIG. 12, the terminal device 18 includes a light receiving circuit 160 that receives downstream infrared light. The light receiving circuit 160 converts the received infrared light into an electrical signal and performs a tuning process on the converted electrical signal to extract one of the downstream FM signals of the two downstream channels CH1 and CH2. Which downlink channel CH1 or CH2 is to be extracted depends on the channel selection control signal given from the control circuit 162 described later. The extracted downlink FM signal is amplified by the RF amplification circuit 164 and then input to the frequency conversion circuit 166.

  A high-frequency signal having a frequency of 12.65 [MHz] or 12.95 [MHz] is also input to the frequency conversion circuit 166 from the local oscillation circuit 168. Which frequency of the high-frequency signal is input depends on the above-described channel selection control signal. Then, the frequency conversion circuit 166 mixes the downlink FM signal input from the RF amplification circuit 164 with the high frequency signal input from the local oscillation circuit 168, and converts it to an intermediate frequency signal having a frequency of 10.7 [MHz]. To do. The converted intermediate frequency signal is amplified by an IF (intermediate frequency) amplifier circuit 170 and then input to the demodulation circuit 172.

  The demodulation circuit 172 performs demodulation processing on the input intermediate frequency signal to generate the above-described mixed signal (downstream audio signal on which the subcarrier signal is superimposed). Then, this mixed signal is input to a separation circuit 174 as separation means, where it is separated into a downlink audio signal and a subcarrier signal. Among these, the downstream audio signal is input to the above-described monitor speaker via the AF amplifier circuit 176. As a result, the sound of the channel CH1 or CH2 is output from the monitor speaker. On the other hand, the subcarrier signal is input to a data demodulating circuit 178 where it is demodulated. As a result, the downlink control data is reproduced, and the reproduced downlink control data is input to the control circuit 162.

  The control circuit 162 has a CPU and analyzes the downlink control data input from the data demodulation circuit 178. Here, for example, when the downlink control data is addressed to itself (including its own identification number) and includes information indicating that the speech is permitted, the control circuit 180 validates the output of the microphone 16. The switching circuit 180 is controlled as described above. In other words, the upstream audio signal output from the microphone 16 is input to the switching circuit 180 via the AF amplifier circuit 182, and the control circuit 180 is configured so that the upstream audio signal is input to the modulation circuit 184. 180 is controlled. The control data also includes information for designating one of the uplink audio channels CH1 to CH4, and the control circuit 180 controls the local oscillation circuit 186 according to the designation information. As a result, a high frequency signal having a frequency of 7.35 [MHz], 8.10 [MHz], 8.55 [MHz], or 9.15 [MHz] is output from the local oscillation circuit 186, and this high frequency signal is modulated. Input to the circuit 184.

  The modulation circuit 184 modulates the frequency of the high frequency signal input from the local oscillation circuit 186 with the upstream audio signal input from the switching circuit 184. As a result, an upstream FM signal is generated. The upstream FM signal is amplified by the RF amplifier circuit 188 and then input to the light transmission circuit 190. The light transmission circuit 190 includes the above-described infrared light emitting diode as a light emitting unit, and causes the infrared light emitting diode to emit light according to the uplink FM signal input from the RF amplification circuit 188. Thereby, infrared rays are emitted from the infrared light emitting diodes. Note that a plurality of infrared light emitting diodes are also provided in the same manner as the infrared light emitting diodes in the light transmitting / receiving device 14 described above, and the plurality of infrared light emitting diodes emit infrared rays in different directions. Therefore, they are arranged in different directions.

  The control circuit 162 is also connected to the above-described operation panel. When the above-described speech request switch provided on the operation panel is operated, the data generation circuit 192 is controlled to indicate that effect. Data is generated and the switching circuit 180 is controlled so that the output of the data generation circuit 192 is validated. As a result, control data is input to the modulation circuit 184 via the switching circuit 180. In addition, the control circuit 162 controls the local oscillation circuit 186 to output a high frequency signal having a frequency of 6.45 [MHz] according to the control channel CH0. This high frequency signal is also input to the modulation circuit 184. As a result, an uplink FM signal based on the control data is generated, and this uplink FM signal is converted into infrared rays and emitted as described above.

  Further, the control circuit 162 generates a channel selection control signal in accordance with the operation of the channel selection switch provided on the above-described operation panel. Then, the channel selection control signal is input to the light receiving circuit 160 and the local oscillation circuit 168 as described above. As a result, the sound of one downstream audio channel CH1 or CH2 according to the channel selection control signal is output from the monitor speaker. Is done.

  Here, the light receiving circuit 160 will be described in more detail. The light receiving circuit 160 is configured as shown in FIG. As shown in FIG. 13, the light receiving circuit 160 includes a plurality of photodiodes 300 as light receiving means in the same manner as the light receiving circuit 156 (photoelectric conversion circuits 220 and 220a) of the light transmitting / receiving device 14 shown in FIG. For example, it has four. These photodiodes 300, 300,... Are connected in parallel to each other, and a DC power supply voltage Vcc is applied to each cathode terminal. The anode terminal of each photodiode 300, 300,... Is connected to the ground potential via one of the two coils 302 and 304. That is, a reverse bias voltage is applied to each of the photodiodes 300, 300,. Note that the selection of the coil 302 or 304 to which the anode terminal is connected to the ground potential is switched by the changeover switch 306, and the operation of the changeover switch 306 is controlled by the above-described channel selection control signal. The DC power supply voltage Vcc is generated by a power supply circuit (not shown) using a battery (not shown) as a power supply source.

  According to this configuration, the tuning circuit 308 capable of switching the tuning frequency is formed by the photodiodes 300, 300,..., The two coils 302 and 304, and the changeover switch 306. The tuning frequency by the tuning circuit 308 is switched according to the operation of the changeover switch 306, that is, the channel selection control signal. Specifically, for example, when the coil 302 is selected (connected to the ground potential) according to the channel selection control signal, the tuning frequency of the tuning circuit 308 is a frequency according to the downlink channel CH1, that is, 1.95 [MHz]. Further, the inductance of the coil 302 is set so as to achieve such a tuning frequency. On the other hand, when the coil 304 is selected according to the channel selection control signal, the tuning frequency is a frequency according to the downstream channel CH2, that is, 2.25 [MHz], and the inductance of the coil 304 is set so as to be the tuning frequency. ing. Accordingly, the tuning circuit 308 outputs the downlink FM signal of the downlink channel CH1 or CH2 according to the channel selection control signal at a high signal level (selectivity).

  The downlink FM signal output from the tuning circuit 308 is input to the preamplifier circuit 312 via the coupling capacitor 310, similarly to the photoelectric conversion circuits 220 and 220a in FIG. This preamplifier circuit 312 has FETs 314, three resistors 316, 318, 320 and a capacitor 322 similar to the preamplifier circuits 230 and 230a in the photoelectric conversion circuits 220 and 220a. Then, the downstream FM signal amplified by the preamplifier circuit 312 is input as an output signal of the light receiving circuit 160 to the RF amplifier circuit 164 of FIG. 12 via the DC cut capacitor 324. In the vicinity of the preamplifier circuit 312, the power supply line (Vcc) is connected to the ground potential via a bypass capacitor 326.

  As described above, in the light receiving circuit 160, the tuning circuit 308 capable of switching the tuning frequency is provided, and the tuning frequency is determined according to the channel selection control signal, that is, according to the operation of the channel selection switch. Or it is set to the reference frequency of CH2. Therefore, it is possible to extract the downlink FM signals of the arbitrary downlink channels CH1 and CH2 with high selectivity, and as a result, it is possible to obtain high reception sensitivity in the arbitrary downlink channels CH1 and CH2.

As can be seen from the above description, according to the light transmitting / receiving device 14 in the first reference example , a plurality of tuning circuits 226 and 226 a are provided in the light receiving circuit 156. The tuning circuits 226 and 226a are tuned so that the overall tuning level becomes a level necessary and sufficient for obtaining good reception sensitivity in all the upstream channels CH0 to CH4. The tuning frequencies f1 and f2 of 226a are set. Therefore, higher sensitivity and a wider reception bandwidth can be obtained as compared with the above-described conventional technology that employs Q dump processing.

  Further, it is not necessary for each terminal device 16 to receive both downlink channels CH1 and CH2 at the same time, as long as only one downlink channel CH1 or CH2 according to the operation of the channel selection switch can be received satisfactorily. It ’s enough. Therefore, the tuning circuit 308 in the light receiving circuit 160 tunes only to the one downstream channel CH1 or CH2. Therefore, each of the two downlink channels CH1 and CH2 can be received with higher sensitivity than before. Also, the received downlink channels CH1 and CH2 include downlink audio signals and downlink control data. That is, these downlink audio signals and downlink control data can be received with the same sensitivity. In other words, for example, the downlink audio signal is normally transmitted and received between the transmitter / receiver device 14 and the terminal device 16, but the downlink control data is not normally transmitted and received. The reliability of communication between the light transmitting / receiving device 14 and the terminal device 16 is improved.

In the first reference example , the light receiving circuit 156 on the side of the light transmitting / receiving device 14 is configured as shown in FIG. 6, but the present invention is not limited to this. For example, as shown in FIG. 14, photoelectric conversion circuits 220 and 220a similar to those in FIG. 6 are provided for each photodiode 222 or 222a, and a plurality of these (total of eight) photoelectric conversion circuits 220, 220,. , 220a, 220a,... May be added by an adder circuit 246. However, in this case, since the number of photodiodes 222 or 222a constituting each photoelectric conversion circuit 220 or 220a (tuning circuit 226 or 226a) is different from that in FIG. 6, the coils constituting the photoelectric conversion circuit 220 or 220a are different. The inductance value of 224 or 224a is also different from the value in FIG.

  Further, instead of the preamplifier circuits 230 and 230a in FIG. 6, for example, a circuit 350 having the configuration shown in FIG. 15 may be employed. That is, as described above, since the light transmission / reception device 14 uses the DC power supplied from the center device 12 as a driving power supply, it is desirable that the power consumption of the light transmission / reception device 14 is as small as possible. Further, since the intensity of the upstream infrared light incident on the light transmitting / receiving device 14 is very small, it is necessary to convert the weak infrared light into an electrical signal (upstream FM signal) having a relatively high level. That is, it is necessary to convert weak upstream infrared light into an electrical signal having a high level while suppressing power consumption of the light transmitting / receiving device 14. Therefore, as shown in FIG. 15, an emitter follower circuit 354 and a high-frequency amplifier circuit 356 are provided in the subsequent stage of the circuit 352 similar to the preamplifier circuits 230 and 230a in FIG.

  More specifically, the first stage circuit 352 includes an FET 358, resistors 360, 362, 364 and a capacitor 366 similar to the preamplifier circuits 230 and 230a in FIG. Thus, by adopting the FET 358 which is a high input impedance element, the output signals of the photodiodes 222, 222,... And 222a, 222a,. The output signal of the first stage circuit 352 (the signal output from the drain terminal of the FET 358) is input to the next-stage emitter follower circuit 354 via the DC cut capacitor 368, and more specifically, the emitter follower circuit 354. Is input to the base terminal of an NPN transistor 370 constituting the circuit. As will be described later, the power for driving the first stage circuit 352 is supplied to the first stage circuit 352 via the emitter follower circuit 354 and the high frequency amplifier circuit 356. For this reason, the other end of the resistor 360 whose one end is connected to the drain terminal of the FET 358 is connected to the emitter terminal of the transistor 370 via the resistor 372 for grounding the emitter constituting the emitter follower circuit 354. The other end of the resistor 360 (a connection point with the resistor 372) is connected to the ground potential via a bypass capacitor 374.

  The emitter follower circuit 354 includes the transistor 370 and the above-described resistor 372 for grounding the emitter, and receives a signal input from the first stage circuit 352 with a high input impedance. An output signal of the emitter follower circuit 354 (a signal output from the emitter terminal of the transistor 370) is input to the final-stage high-frequency amplifier circuit 356 via the DC-cut capacitor 376. The signal is input to the base terminal of the NPN transistor 378 constituting the circuit 356. A DC bias voltage is applied to the base terminal of the transistor 370, which is the input terminal of the emitter follower circuit 354. Specifically, the base terminal is connected to the power supply line (Vcc) via the resistors 380 and 382. And connected to the ground potential via a resistor 384. As will be described later, power for driving the emitter follower circuit 354 is supplied to the emitter follower circuit 354 via the high frequency circuit 356. For this reason, the collector terminal of the transistor 370 is connected to the emitter terminal of the transistor 370. The collector terminal is also connected to the ground potential via a bypass capacitor 386.

  The high-frequency amplifier circuit 356 includes a transistor 378 and a power supply resistor 388 connected between the drain terminal of the transistor 378 and a power supply line. The three resistors 380, 382 and 384 described above also function as bias resistors for applying a DC bias voltage to the base terminal of the transistor 378. Specifically, the resistors 380 and 382 are interconnected. The base terminal is connected to the point. In the vicinity of the high-frequency amplifier circuit 356, the power supply line is connected to the ground potential via a bypass capacitor 390. Then, the output signal of the high-frequency amplifier circuit 356 (the signal output from the collector terminal of the transistor 378) is output to the adder circuit 246 of FIG. 6 as an output signal of the entire preamplifier circuit 350 shown in FIG. (Via capacitor 244 or 244a).

  According to the preamplifier circuit 350 configured as described above, in terms of direct current, the power supply line includes the resistor 388, the collector terminal-emitter terminal of the transistor 378, the collector terminal-emitter terminal of the transistor 370, the resistor 372, the resistor 360, and the drain terminal-source terminal of the FET 358 and the resistor 364 are connected to the ground potential. Therefore, as indicated by a dotted arrow 392 in FIG. 15, a drive current Id for driving the high frequency amplifier circuit 356, the emitter follower circuit 354, and the first stage circuit 352 flows through these circuits 356, 354, and 352. That is, these circuits 352, 354 and 356 are driven by supplying a common drive current Id (drive power). Therefore, the power consumption of the entire preamplifier circuit 350 is suppressed accordingly. Note that the voltage value Vcc of the power supply line is desirably set to a relatively high value, for example, approximately +15 [V] to +24 [V]. In this way, the drive current Id can be suppressed to about 1 [mA].

  Further, as shown in FIG. 15, an FET 358 which is a high input impedance element is adopted for the first stage circuit 352, and the output signal of the first stage circuit 352 is amplified at the final stage via an impedance conversion emitter follower circuit 354. By inputting to the circuit 356, the amplification factor of the high-frequency amplifier circuit 356 can be increased. As a result, the preamplifier circuit 350 as a whole can obtain an extremely large amplification factor of, for example, about 50 [dB].

  That is, by adopting the preamplifier circuit 350 shown in FIG. 15, the light transmitting / receiving device 14 that can receive weak upstream infrared light (upstream FM signal) with better sensitivity while having low power consumption, Can be realized. The configuration shown in FIG. 15 can also be applied to the light receiving circuit 160 on the terminal device 18 side. That is, instead of the preamplifier circuit 312 in FIG. 13, the circuit 350 in FIG. 15 may be employed.

Further, in the first reference example, as shown in FIGS. 9 to 11 described above, the low-frequency side of the photodiode 222 and 222, ... and a group of high frequency side of the photodiode 222a, 222a, ... a group of Are arranged in directions different from each other by 45 degrees, but are not limited thereto. For example, as shown in FIG. 16, a group of these low-frequency side photodiodes 222, 222,... And a group of high-frequency side photodiodes 222a, 222a,. Also good. In this case, as shown in FIG. 16, the low-frequency side photodiodes 222, 222,... And the high-frequency side photodiodes 222a, 222a,... Are arranged side by side (in a direction along the plane of FIG. 16). ) May be arranged, or may be arranged so as to overlap in the vertical direction (the front and back direction in FIG. 16).

  As shown in FIG. 2 described above, one control channel CH0 and four audio channels CH1 to CH4 are provided as uplink channels, but other channel numbers may be used. Further, the downlink channel numbers CH1 and CH2 may be other channel numbers. Furthermore, although both the uplink voice signal and the uplink control data (subcarrier signal) are transmitted by each of the downlink channels CH1 and CH2, the present invention is not limited to this. That is, for the downlink channel, a channel dedicated to audio signals and a channel dedicated to control data may be provided separately. The reference frequencies of the uplink channels CH0 to CH4 and the downlink channels CH1 to CH2 are not limited to the values shown in FIG.

In the first reference example , the infrared conference system 10 has been described as an example, but the present invention is not limited to this. That is, it goes without saying that the same technology as that of the first reference example can be applied to a communication device using infrared as a medium.

Next, a second reference example of the present invention will be described.

In the second reference example , the light receiving circuit 160 on the terminal device 14 side is configured as shown in FIG. 17, and a double tuning circuit 400 is used instead of the tuning circuit 308 in FIG. is there. Other configurations, that is, the DC cut capacitor 310, the preamplifier circuit 312 (FET 314, resistors 316, 318, 320, and capacitor 322), the DC cut capacitor 324, and the bypass capacitor 326 are shown in FIG. Since these are the same as those in FIG. The photodiodes 300, 300,... Are also the same as those shown in FIG.

  The double-tuned circuit 400 includes photodiodes 300, 300,..., Two coils 402 and 404, and two capacitors 406 and 408. Specifically, the anode terminals of the photodiodes 300, 300,... Are connected to the ground potential via the coil 402. One end of a capacitor 406 is connected to the connection point between the anode terminals of the photodiodes 300, 300,... And the coil 402, and the other end of the capacitor 406 is connected to the ground potential via the coil 404. ing. A capacitor 408 is connected in parallel with the coil 404. The interconnection point between the coil 404 and the capacitors 406 and 408 is connected to the source terminal of the FET 314, which is the input terminal of the preamplifier circuit 314, via the capacitor 310 as the output terminal of the double tuning circuit 400. Yes.

  An equivalent circuit of such a double-tuned circuit 400 is shown in FIG. As shown in FIG. 18, the photodiodes 300, 300,... Can be represented by a capacitor 410 having a capacitance component C1. A coil 402 is connected in parallel with the capacitor 410, and a parallel circuit of the capacitor 410 and the coil 402 is connected to a parallel circuit of the coil 404 and the capacitor 408 through a capacitor 406. That is, they are electrostatically coupled. The capacitance value C1 of the capacitor 410 is determined by the capacitance and number of the photodiodes 300, 300,..., And the capacitance value C2 of the capacitor 408 is substantially equivalent to the capacitance value C1 of the capacitor 410.

  The double-tuned circuit 400 has frequency characteristics as shown in FIG. That is, as indicated by a solid curve C in FIG. 19, the frequency f1 ′ is close to the reference frequency (1.95 [MHz]) of the downlink channel CH1 and the reference frequency (2.25 [MHz]) of the downlink channel CH2. It has a so-called bimodal characteristic that shows a peak at a near frequency f2 ′. More specifically, one peak frequency f1 ′ is about 1.93 [MHz], which is slightly lower than the reference frequency of the downlink channel CH1, and the other peak frequency f2 ′ is lower than the reference frequency of the downlink channel CH2. Is about 2.28 [MHz], which is a little higher. These peak frequencies f1 'and f2' are determined by the inductance values L1 and L2 of the coils 402 and 408 and the capacitance value CS of the capacitor 406. In particular, by increasing the capacitance value CS of the capacitor 406, a tightly coupled state is established, and two peaks are formed as shown in FIG. For reference, the frequency characteristic of a so-called single tuning circuit having a tuning point at the center frequency (2.10 [MHz]) in the middle of each reference frequency is shown by a dotted curve D in FIG. Further, a frequency characteristic when the above-described Q dump processing is applied to this single tuning circuit is indicated by a curve E.

As can be seen from FIG. 19, according to the double-tuned circuit 400 in the second reference example , compared with the single-tuned circuit, a higher signal level (selection) at the same frequency as the reference frequency of each of the downstream channels CH1 and CH2. Degree). That is, each of the downlink channels CH1 and CH2 can be received with high sensitivity. Further, since both of these downlink channels CH1 and CH2 can be received simultaneously, there is no need to provide the changeover switch 306 as in the first reference example (FIG. 13).

In the second reference example , a frequency of about 1.93 [MHz] slightly lower than the reference frequency of the downlink channel CH1 and about 2.28 [MHz] slightly higher than the reference frequency of the downlink channel CH2. The peak frequencies f1 ′ and f2 ′ are formed at the frequency of the above, but at other frequencies, for example, the reference frequencies (1.95 [MHz] and 2.25 [MHz]), the peak frequency f1 ′ and f2 ′ may be formed. However, as can be seen from FIG. 19, in the double-tuned circuit 400, the slope of the frequency characteristic (outside each peak) is steeper than in the single-tuned circuit. Therefore, in order to obtain high selectivity at the reference frequencies of the downlink channels CH1 and CH2, frequencies (about 1.93 [MHz] and about 2.28 which are slightly shifted from the respective reference frequencies as in the second reference example ). It is effective to form a peak at [MHz]).

Further, as shown by a curve C in FIG. 19, the frequency characteristics of the double-tuned circuit 400 are made to be bimodal characteristics, but the present invention is not limited to this. For example, by making the capacitance value of the capacitor 406 slightly smaller than that in the second reference example , the double-tuned circuit 400 is brought into a so-called critical coupling state, and as a result, the frequency characteristic of the double-tuned circuit 400 becomes flat. It may be.

In the second reference example , the case where the double tuning circuit 400 is applied to the light receiving circuit 160 on the terminal device 18 side has been described. However, the present invention is not limited to this. That is, a similar double-tuned circuit may be applied to the light receiving circuit 156 on the light transmitting / receiving device 14 side. It goes without saying that the same technique as that of the second reference example can be applied to apparatuses other than the infrared conference system 10.

Subsequently, a first embodiment of the present invention will be described.

In the first embodiment , the present invention is applied to an infrared microphone system 500 as shown in FIG. That is, the infrared microphone system 500 includes a plurality of hand-type microphones 502, 502,... As infrared transmission devices. These microphones 502, 502,... Generate FM signals according to the voices input to the respective microphones, further convert the FM signals into infrared rays and emit the infrared signals. The emitted infrared light is incident on a light receiving device 504 as an infrared receiving device, where it is converted into an electrical signal. Further, this electric signal is subjected to a tuning process, whereby an FM signal is extracted. The extracted FM signal is input to the main body device 508 via a coaxial cable 506 serving as a transmission line. The main device 508 performs demodulation processing on the input FM signal to reproduce an audio signal. The reproduced audio signal is input to an external speaker (not shown), thereby reproducing the sound of each microphone 502, 502,.

Note that the reference frequency of the FM signal described above is different for each microphone 502, and for example, a maximum of five frequencies f0 to f4 are prepared as the reference frequency. In other words, in the infrared microphone system 500 of the first embodiment , a maximum of five channels CH0 to CH4 corresponding to the respective reference frequencies f0 to f4 are prepared. Therefore, the light receiving device 504 needs to simultaneously receive the plurality of channels CH0 to CH4, and adopts Q dump processing as a means for realizing the reception. However, the degree of the Q dump process can be changed according to the number of channels actually used (the number of microphones 502), which is greatly different from the above-described conventional technology. The values of the reference frequencies f0 to f4 have a relationship of “f3 <f1 <f0 <f2 <f4”.

  That is, the light receiving device 504 includes a light receiving circuit 510 as shown in FIG. As shown in FIG. 21, the light receiving circuit 510 basically includes the photoelectric conversion shown in FIG. 6 described above except for the three resistors 512, 514 and 516 for Q dump processing and the changeover switch 518. The configuration is the same as that of the circuit 220 (or 220a). Specifically, a plurality of photodiodes 520, 520,... Similar to those shown in FIG. 6 and a coil 524 that forms a tuning circuit 522 together with the plurality of photodiodes 520, 520,. Yes. A coupling capacitor 526 and a preamplifier circuit 528 to which the output signal of the tuning circuit 522 is input via the coupling capacitor 526 are provided. The preamplifier circuit 528 includes an FET 530, three resistors 532, 534, and 536, and two bypass capacitors 538 and 540. The output signal of the preamplifier circuit 528 is input as an output signal of the light receiving circuit 510 to the RF amplifier circuit (not shown) in the subsequent stage through the direct cut capacitor 542. Then, the signal amplified by the RF amplifier circuit is sent to the main device 508 via the coaxial cable 506.

  The resistors 512, 514, and 516 for Q dump processing are provided between the anode terminals of the photodiodes 520, 520,... And the ground potential. Connected to ground potential through any of devices 512, 514 and 516. Which resistor 512, 514 or 516 is connected to the ground potential is switched by manual operation of the changeover switch 518. The resistance values R1, R2, and R3 of the resistors 512, 514, and 516 are different from each other, and have a relationship of “R1> R2> R3”, for example.

The tuning circuit 522 to which the resistors 512, 314, and 316 for Q dump processing and the changeover switch 518 are added has frequency characteristics as shown in FIG. Specifically, in FIG. 22, a curve F indicated by a solid line is a frequency characteristic when the resistor 512 (R1) is selected by the changeover switch 518, that is, when it is activated. A curved line G indicated by a dotted line is a frequency characteristic when the resistor 514 (R2) is activated, and a curved line H indicated by a one-dot chain line is that the resistor 516 (R3) is activated. Is a characteristic.

As can be seen from FIG. 22, the tuning circuit 522 has a tuning point at the same frequency as the reference frequency f0 of the channel CH0. Then, when the resistor 512 is activated, the highest selectivity is obtained, and in particular the selectivity at the peak frequency (f0) is greater than the other frequencies. Therefore, for example, when only one microphone 502 is used, a microphone dedicated to the channel CH0 is used as the microphone 502, and the resistor 512 is activated by operating the changeover switch 518 to emit from the microphone 502. Infrared (FM signal) can be received with very good sensitivity.

When the resistor 514 is activated by the changeover switch 518, the selectivity of the tuning circuit 522 is generally lower than when the resistor 512 is activated, but near the peak frequency, For example, in the range of the reference frequency f1 of the channel CH1 to the reference frequency f2 of the channel CH2, the selectivity (characteristic) is relatively flattened. Therefore, for example, when using up to three microphones 502, the three microphones 502, 502, and 502 are used for channels CH0 to CH2, and the switch 518 is operated to activate the resistor 514. To do. In this way, infrared rays emitted from the microphones 502, 502, 502 can be received with relatively good and uniform sensitivity. In addition, since the receiving sensitivity of the channel CH0 is the highest among the channels CH0 to CH2, it is desirable to preferentially use the microphone 502 dedicated to the channel CH0.

When the resistor 516 is enabled by the changeover switch 518, the selectivity of the tuning circuit 522 is further reduced, but a wider frequency band centered on the peak frequency, for example, the reference frequency f0 of all the channels CH0 to CH4. A relatively flat selectivity is obtained in the band including ˜f4. Therefore, when the microphones 502, 502,... Of all the channels CH0 to CH4 are used, the resistor 516 may be validated. However, the reception sensitivity in each channel CH0 to CH4 gradually decreases in the order of channel CH0 → channel CH1 (or CH2) → channel CH2 (or CH1) → channel CH3 (or CH4) → channel CH4 (or CH3). Therefore, it is desirable to prioritize the use of each microphone 502, 502,... Based on this order.

Thus, according to the first embodiment , the degree of the Q dump process can be changed according to the number of channels (microphones 502) that are actually used. Therefore, the infrared receiving sensitivity of the light receiving device 504 can always be optimized according to the number of channels.

In the first embodiment , the infrared microphone system 500 shown in FIG. 20 has been described as an example, but the present invention is not limited to this. For example, the same technique as the first embodiment may be applied to the infrared conference system shown in FIG.

Next, a second embodiment of the present invention will be described.

In the second embodiment , a light receiving circuit 600 shown in FIG. 23 is applied to the receiving device 504 in FIG. 20 instead of the light receiving circuit 510 shown in FIG. That is, as shown in FIG. 23, the light receiving circuit 600 has a plurality of, for example, three photoelectric conversion circuits 602, 602a, and 602b similar to the photoelectric conversion circuit 220 (or 220a) shown in FIG. . Specifically, for example, the photoelectric conversion circuit 602 shown at the top in FIG. 23 includes a plurality of photodiodes 604, 604,... Similar to those shown in FIG. And a coil 608 constituting a tuning circuit 606. A coupling capacitor 610 and a preamplifier circuit 612 to which the output signal of the tuning circuit 606 is input via the coupling capacitor 610 are provided. The preamplifier circuit 612 includes an FET 614, three resistors 616, 618 and 620, and two bypass capacitors 622 and 624. Then, the output signal of the preamplifier circuit 612 is input as an output signal of the photoelectric conversion circuit 602 to the adder circuit 628 as a synthesizing unit via the capacitor 626 for direct cut. Specifically, the adder circuit 628 is described in detail. Is input to the inverting input terminal of the operational amplifier 632 through the input resistor 630. The inverting input terminal of the operational amplifier 632 is connected to the output terminal of the operational amplifier 632 via the feedback resistor 634, and the non-inverting input terminal is connected to the ground potential.

  The photoelectric conversion circuit 602a shown second from the top in FIG. 23 is also similar to the photoelectric conversion circuit 602 described above, the photodiodes 604a, 604a,..., The coil 608a, the coupling capacitor 610a, and the preamplification. A circuit 612a (FET 614a, resistors 616a, 618a, 620a, capacitors 622a and 624a) is included. Further, a tuning circuit 606a is configured by the photodiodes 604a, 604a,... And the coil 608a. The output signal of the preamplifier circuit 612a is input to the inverting input terminal of the operational amplifier 632 through the capacitor 626a and the resistor 630a as the output signal of the photoelectric conversion circuit 602a. Note that a manual series switch 636a is provided between the inverting input terminal of the operational amplifier 632 and the resistor 630a so as to connect or disconnect them from each other.

  Similarly, the photoelectric conversion circuit 602b shown at the bottom in FIG. 23 also has photodiodes 604b, 604b,. , Capacitors 622b and 624b). Further, a tuning circuit 606b is configured by the photodiodes 604b, 604b,... And the coil 608b. The output signal of the preamplifier circuit 612b is input to the inverting input terminal of the operational amplifier 632 through the capacitor 626b and the resistor 630b as the output signal of the photoelectric conversion circuit 602b. A series switch 636b similar to that described above is also provided between the inverting input terminal of the operational amplifier 632 and the resistor 630b.

  Then, the output signal of the adder circuit 626 (the operational amplifier 630) is input as an output signal of the light receiving circuit 600 to an RF amplifier circuit (not shown) in the subsequent stage.

  Here, the tuning circuits 606, 606a and 606b of the photoelectric conversion circuits 602, 602a and 602b have tuning points at different frequencies. Specifically, the tuning circuit 606 of the photoelectric conversion circuit 602 has the same frequency as the lowest reference frequency f3 among the reference frequencies f0 to f4 of the channels CH0 to CH4, as indicated by a solid curve J in FIG. Has a tuning point. Then, the tuning circuit 606a of the photoelectric conversion circuit 602a sets the tuning point to the same frequency as the central reference frequency f0 among the reference frequencies f0 to f4 of the channels CH0 to CH4, as indicated by a dotted curve K in FIG. Have. Then, the tuning circuit 606b of the photoelectric conversion circuit 602b has a tuning point at the same frequency as the highest reference frequency f4 among the reference frequencies f0 to f4 of the channels CH0 to CH4, as indicated by a dashed line L in FIG. have. The tuning points (tuning frequencies) of these tuning circuits 606, 606a and 606b are adjusted by the inductance values of the coils 608, 608a and 608b.

  According to such a configuration, even if the respective series switches 636a and 636b are turned off (opened), the frequency characteristics (selectivity) indicated by the curve J in FIG. Therefore, for example, when only one microphone 502 is used, the infrared ray (FM signal) emitted from the microphone 502 is received with very good sensitivity by using the microphone 502 dedicated to the channel CH3. Can do.

  When the series switch 636a is turned on (closed), in addition to the frequency characteristic indicated by the curve J described above, the frequency characteristic indicated by the curve K is additionally obtained as a whole of the light receiving circuit 600, and these curves are also obtained. A frequency characteristic indicated by a two-dot chain curve M complemented by J and K is also obtained. Therefore, for example, when up to three microphones 502 are used, the three microphones 502, 502 and 502 may be used for channels CH3, CH1 and CH0 and the series switch 636a may be turned on. At this time, each of the tuning circuits 606 described above is selected so as to obtain a selectivity higher than a predetermined level S necessary for obtaining good reception sensitivity in all channels CH3, CH1 and CH0 to be received. And the tuning frequency of 606a is set.

  Further, when both series switches 636a and 636b are turned on, the light receiving circuit 600 as a whole can additionally obtain the frequency characteristics indicated by the curve L in addition to the frequency characteristics indicated by the curves J, K and M described above. In addition, a frequency characteristic indicated by a two-dot chain line curve N complemented by these curves K and L is also obtained. Therefore, when all the microphones 502, 502,... Of channels CH0 to CH4 are used, both series switches 636a and 636b may be turned on. At this time, the tuning frequencies of the tuning circuits 606a and 606b are set so that the selectivity of the predetermined level S or higher can be obtained also in the channels CH2 and CH4.

As described above, according to the second embodiment , a plurality of tuning circuits 606, 606a, and 606b having different tuning frequencies are provided, and the plurality of tuning circuits 606 are selected according to the number of microphones 502 that are actually used. , 606a and 606b (photoelectric conversion circuits 602, 602a and 602b) are individually activated. Then, each tuning circuit 606, 606a and 606a and 606a and 606 that have been validated are equal to or higher than a predetermined level S in the channel for the microphone 502 that is actually used. A tuning frequency of 606 is set. Therefore, higher sensitivity and wider reception bandwidth can be obtained as compared with the prior art employing Q dump processing.

In the second embodiment , three photoelectric conversion circuits 604, 604a, and 604b are provided. However, other numbers of photoelectric conversion circuits may be provided.

  In addition, when each of the series switches 636a and 636b is turned off, a switch circuit for turning off the supply of the power supply voltage Vcc to each of the photoelectric conversion circuits 604a and 604b may be provided in conjunction with this. In this way, the power consumption of the light receiving device 504 can be reduced according to the number of microphones 502 actually used.

It is a block diagram which shows schematic structure of the 1st reference example of this invention. It is an illustration figure which shows the list of the channels used for communication in the said 1st reference example . It is a block diagram which shows the internal structure of the center apparatus in FIG. It is a block diagram which shows the detail of the transmission circuit in FIG. It is a block diagram which shows the internal structure of the light transmission / reception apparatus in FIG. FIG. 6 is an electric circuit diagram showing details of the light receiving circuit in FIG. 5. It is an illustration figure which shows the frequency characteristic of the light receiving circuit of FIG. It is a figure which shows the external appearance and directivity characteristic of the photodiode in FIG. It is an illustration figure which shows the arrangement | positioning relationship of the photodiode in FIG. FIG. 7 is an illustrative view in which directivity characteristics of each photodiode are added to FIG. 6. It is an illustration figure which represented the directional characteristic of FIG. 10 whole. It is a block diagram which shows the internal structure of the terminal device in FIG. FIG. 13 is an electric circuit diagram showing details of the light receiving circuit in FIG. 12. FIG. 7 is an electric circuit diagram showing a configuration example different from FIG. 6. FIG. 7 is an electric circuit diagram showing another configuration example of the preamplifier circuit in FIG. 6. It is an illustration figure which shows the arrangement | positioning relationship and directivity different from FIG. It is an electrical circuit diagram which shows the detail of the light receiving circuit by the side of the terminal device in the 2nd reference example of this invention. FIG. 18 is an equivalent circuit diagram of the double-tuned circuit in FIG. 17. It is an illustration figure which shows the frequency characteristic of the light receiving circuit of FIG. It is a block diagram which shows schematic structure of 1st Embodiment of this invention. It is an electric circuit diagram which shows the detail of the light receiving circuit in the light-receiving device in FIG. It is an illustration figure which shows the frequency characteristic of the light receiving circuit of FIG. It is an electric circuit diagram which shows the detail of the light-receiving circuit in the light-receiving device in 2nd Embodiment of this invention. It is an illustration figure which shows the frequency characteristic of the light receiving circuit of FIG. It is a block diagram which shows schematic structure of the conventional wireless microphone system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Infrared conference system 12 Center apparatus 14 Transmission / reception apparatus 18 Terminal apparatus 222 Photodiode 224 Coil 226 Tuning circuit 246 Adder circuit

Claims (3)

In an infrared receiving apparatus for simultaneously receiving one or more high frequency signals having different reference frequencies transmitted using infrared as a medium,
A light receiving means for receiving the infrared light and converting it into an electrical signal;
Tuning means for inputting the electrical signal converted by the light receiving means and performing tuning processing on the electrical signal ;
Characteristic control means including a changeover switch that can be manually changed, and changing the frequency characteristic of the tuning means in accordance with the operation of the changeover switch;
Comprising
The tuning means has a tuning frequency between the lowest reference frequency and the highest reference frequency.
The characteristic control means changes a Q value of the frequency characteristic of the tuning means;
An infrared receiver. In an infrared receiving apparatus for simultaneously receiving one or more high frequency signals having different reference frequencies transmitted using infrared as a medium,
A plurality of light receiving means for receiving the infrared rays and converting them into electrical signals;
A plurality of tuning means that are provided corresponding to each of the light receiving means and that receive the electrical signals converted by the corresponding light receiving means and that perform tuning processing on the electrical signals ;
And enabling means for enabling individual manual on SL plurality of tuning means,
Combining means for combining the output signals of the tuning means validated by the validation means;
Comprising
The plurality of tuning means have tuning frequencies at different frequencies in a first frequency band from the lowest reference frequency to the highest reference frequency;
When two tuning means adjacent to each other among the plurality of tuning means are activated by the enabling means, each frequency in the second frequency band from one of the two adjacent tuning frequencies to the other is selected. The frequency characteristics of each of the plurality of tuning means are set so that the output level of the synthesizing means is equal to or higher than a predetermined level and one or more reference frequencies exist in the second frequency band,
The number of tuning means is less than the number of infrared transmission devices on the infrared transmission side;
An infrared receiver. The tuning means is driven by being supplied with a power supply voltage,
A switch that turns off the supply of the power supply voltage to the deactivated tuning means in conjunction with the invalidation when any of the tuning means is deactivated by the validation means Further comprising a circuit,
The infrared receiver according to claim 2.

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