JPH065845B2 - Transmission / reception switching device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission / reception switching device suitable for a so-called speakerphone or the like, which is mounted on a telephone in a desk-top handset to switch transmission / reception.

2. Description of the Related Art In such a half-duplex type call switching device, a transmission / reception mode is selectively switched according to a signal level between transmission / reception systems.

Therefore, even if the signal of each transmission / reception system is an unnecessary signal other than the call signal, for example, a noise signal, the noise signal is the target of the level comparison. If the level of the desired signal component is higher than the level of the required signal component, there is a drawback of transmitting or receiving the unnecessary signal side.

For example, if there is a motor or other noise source near the telephone, and the noise level exceeds the voice level, the switching of transmission / reception is dominated by the noise level, and transmission / reception of the voice signal, which is a necessary signal component, is disturbed. May be

Therefore, the present invention determines whether or not it is a necessary signal, and performs transmission / reception switching by comparing necessary signals between transmission / reception systems, and eliminates the influence of unnecessary signal components such as noise to perform transmission / reception switching. It is an object of the present invention to provide a transmission / reception switching device with improved reliability.

Means for Solving the Problems That is, the transmission / reception switching device of the present invention includes a microphone (14) for inputting a voice to be transmitted, a speaker (28) attached to the microphone for reproducing a voice, and Is installed in a transmission system (4) for transmitting the transmission signal of the above to the line side, and a transmission side signal switching circuit (current control amplifier 18) for passing or blocking the transmission signal, and a reception system for receiving the reception signal from the line side ( 6), which compares the levels of the transmission signal and the reception signal with a reception side signal switching circuit (current control amplifier 24) installed in 6) for passing or blocking the reception signal, and generating an output representing the comparison result (30) and a signal determination circuit (transmission side) that determines the presence or absence of a voice signal by receiving the transmission signal from the transmission system or the reception signal from the reception system. The signal discriminating circuit 34, the receiving side signal discriminating circuit 36), and the transmitting side signal switching circuit or the receiving side signal switching circuit is selectively turned on or off by the comparison output of the comparator and the discriminating output of the signal discriminating circuit. In a transmission / reception switching device including a switching control circuit (32) for switching to a signal cutoff state, the signal determination circuit receives the transmission signal or the reception signal and performs logarithmic compression on the transmission signal or the reception signal. An amplifier (a differential amplifier 38 and a diode 42), a transistor (44) whose output is added to the base and takes out a signal current corresponding to the signal to be discriminated, and is charged with the signal current through this transistor. A voice to be discriminated, which comprises a first capacitor (50) and a first resistor (52) whose discharging voltage should be discharged. First time constant corresponding to the frequency of the No. (tau _S)
And a voltage dividing circuit (resistors 54, 56) to which the charging voltage of the first capacitor is applied through the first buffer circuit (46) and the charging voltage is divided and taken out. And a second resistor (6
4) and a series circuit of a second capacitor (66), a second time constant (τ _S ) corresponding to the interval of the audio signal is set, and the second resistor and the second capacitor are connected. At a point, a second time constant circuit to which the output of the first buffer circuit is applied through a second buffer circuit (58) and a diode (62), a charging voltage of the second capacitor, and the voltage dividing circuit. A comparison means (differential amplifier 6) that compares the extracted DC voltage and extracts an output representing the magnitude relationship between the two as an audio signal discrimination output (72).
8) and are provided.

Therefore, in the transmission / reception switching device of the present invention, the presence / absence of the voice signal is determined by whether or not the signal passing through the transmission system and the reception system is on the predetermined level in the frequency range that the voice signal should have, and the determination output , And a comparison output for comparing signal levels between the respective systems are added to the switching control circuit. When the necessary signal components are present in both the transmission and reception systems, the levels of the respective signal components are compared by a comparator, and transmission / reception switching is performed based on the comparison output.

The necessary signal component, that is, the audio signal is discriminated by the signal discriminating circuit. In the signal discrimination circuit, the signal to be discriminated from the transmission system or the reception system is added to the amplifier and logarithmically compressed. The output of this amplifier is converted into a signal current by the transistor, and this signal current flows through the first capacitor in the first time constant circuit. Since the first time constant set in the first time constant circuit corresponds to the frequency of the voice signal, when the voice signal arrives, the first capacitor keeps the voltage constant due to the signal current. Be charged.

The charging current of the capacitor is applied to the voltage dividing circuit through the first buffer circuit to be divided, and is also applied to the connection point of the resistor and the capacitor in the second time constant circuit through the second buffer circuit and the diode. .

The second capacitor of the second time constant circuit is charged via the second resistor. Since the time constant corresponds to the interval of the audio signal, the charging voltage of the second capacitor is the first voltage. When it exceeds the charging voltage of the capacitor, the charging voltage is discharged through the diode and the second buffer circuit. The charging voltage of the second capacitor and the charging voltage of the first capacitor applied through the voltage dividing circuit are compared by a comparison means, and the comparison result is taken out as a judgment output indicating the presence / absence of an audio signal. This judgment output is applied to the switching control circuit to switch between the transmission system and the reception system.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the transmission / reception switching device of the present invention.

In FIG. 1, the transmission / reception switching device is provided with a signal transmission / reception circuit 2 for transmitting / receiving a call signal, and the signal transmission / reception circuit 2 is provided with telephone lines L ₁ and L ₂ and a telephone exchange (not shown). The other party's telephone is connected, and the transmission system 4 and the reception system 6 installed inside the transmission / reception switching device are also connected.

The signal transmission / reception circuit 2 is a hybrid circuit 8 called a speech network to which a rectifier circuit 10 composed of a diode bridge circuit is connected, and sends a transmission signal from a transmission system 4 to telephone lines L ₁ and L ₂ . , Or the signals sent from the telephone lines L ₁ and L ₂ are received and added to the receiving system 6.

A common handset 12 is installed in the transmission system 4 and the reception system 6, and a microphone 14 for inputting a voice to be transmitted and a speaker 28 for reproducing a reception signal as a voice are provided in the handset 12. The transmission system 4, after amplifying the audio signal obtained by the microphone 14 by the amplifier 16, adds to the current control amplifier 18 as a transmission side signal switching circuit that passes or blocks the amplified output, and also passes the current control amplifier 18. This is a signal system in which the signal is amplified by the amplifier 20 and sent from the signal transmission / reception circuit 2 to the telephone lines L ₁ and L ₂ .

Further, the receiving system 6 arrives via the telephone lines L ₁ and L ₂ , amplifies the signal received by the signal transmission / reception circuit 2 by the amplifier 22, and then uses a current as a receiving side signal switching circuit for passing or blocking the signal. In addition to the control amplifier 24, the signal system that amplifies the signal that has passed through the current control amplifier 24 by the amplifier 26 and adds the amplified output to the speaker 28 of the handset 12 to reproduce voice.

With the transmission signal from the transmission system 4 on the output side of the current control amplifier 18, the output side of the amplifier 222, that is,
The received signal from the receiving system 6 at the input side of the current control amplifier 24 is applied to the comparator 30, and the level comparison output is applied to the switching control circuit 32 which increases or decreases the amplification gain of the current control amplifiers 18 and 24. This switching control circuit 3
2 uses the comparison output from the comparator 30 as a switching control input to generate a mode switching signal and selectively increase or decrease its amplification gain. That is, the operating currents of the current control amplifiers 18 and 24 are switched by the mode switching signal current, and the amplification gain thereof is selectively increased or decreased to be switched to the signal passing state or the blocking state. Each of the current control amplifiers 18 and 24 may be composed of a voltage control amplifier (VCA) or a current control attenuator (CCA). In the case of being composed of the voltage control amplifier, the switching control circuit 32 is of a voltage output type. By doing so, similar switching control is possible, and in the case of a current control attenuator,
The amount of attenuation is continuously controlled by the output of the comparator 30.

In this transmission / reception switching device, the transmission side signal discriminating circuit 3 for discriminating whether the transmission signal of the transmission system 4 on the input side of the current control amplifier 18 is a necessary signal component or an unnecessary signal component.
4 is installed and the reception side signal discriminating circuit 36 for discriminating whether the reception signal of the reception system 6 at the input side of the current control amplifier 24 is a necessary signal component or an unnecessary signal component.
Is installed. Here, the necessary signal component means a signal component having necessary information such as a voice signal, and the unnecessary signal component means an interfering signal component such as noise other than the necessary signal component.

The operation will be described based on the above configuration.

The handset 12 is connected to the partner telephone via the transmission system 4, the reception system 6, the signal transmission / reception circuit 2, the telephone lines L ₁ and L ₂ and the telephone exchange.

In such a connection state, the voice signal received by the microphone 14 of the handset 12 is amplified by the amplifier 16, and then added to the current control amplifier 18 and the transmission side signal determination circuit 34. Current control amplifier 18
The signal passed through is added to the amplifier 20 and
The amplified output of the amplifier 20, which is applied to the comparator 30, is sent from the hybrid circuit 8 and the rectifier circuit 10 of the signal transmission / reception circuit 2 to the telephone lines L ₁ and L ₂ .

Then, the transmission-side signal discrimination circuit 34 discriminates the presence or absence of an audio signal depending on whether or not the signal passing through the transmission system 4 is at or above a predetermined level in the frequency range that the audio signal should have. , Generate high level decision output.

The voice signals sent from the telephone lines L ₁ and L ₂ are rectified by the rectifying circuit 10 of the signal transmitting / receiving circuit 2, pass through the hybrid circuit 8, are amplified by the amplifier 22, and are then current controlled amplifier. 24, a comparator 30, and a receiving side signal discriminating circuit 36.

Then, the reception side signal discrimination circuit 36 discriminates the presence or absence of an audio signal depending on whether or not the signal passing through the reception system 6 is equal to or higher than a predetermined level in the frequency range that the audio signal should have. , Generate high level decision output.

Further, the comparator 30 compares the levels of the signals applied from the transmission system 4 and the reception system 6, and when the level of the transmission signal is higher than that of the reception signal, a positive comparison output proportional to the difference is output. In addition to the switching control circuit 32, the transmission mode is set in this case. On the contrary, when the reception signal level is higher than the transmission signal level, the reception mode is set, and a negative comparison output proportional to the difference is added to the switching control circuit 32.

That is, the comparison output of the comparator 30 and the discrimination outputs of the transmission side signal discrimination circuit 34 and the reception side signal discrimination circuit 36 are added to the switching control circuit 32, respectively, and the transmission control mode is transmitted from the switching control circuit 32 based on these outputs. A switch signal is applied to the current control amplifier 18, or a receive mode switch signal is applied to the current control amplifier 24. In this case, the comparator 30 simply compares the signal levels between the transmission / reception systems 4 and 6 and generates a comparison output according to the level difference, whereas the transmission / reception side signal determination circuits 34 and 36 generate the respective signals. Only when there is a required signal component of the signals of the systems 4 and 6, that is, a voice signal, the judgment output is generated. Therefore, when an audio signal is present in both the transmission / reception systems 4 and 6, the switching control circuit 32 generates a transmission or reception mode switching signal based on the comparison output of the comparator 30, and
When the required signal component does not exist in the transmission system 4 or the reception system 6, the transmission system 4 on the side where the normal audio signal component exists regardless of the level comparison output of the comparator 30.
Alternatively, a transmission mode switching signal or a reception mode switching signal is generated in order to put the receiving system 6 into an operating state. In other words, the presence of the audio signal is prioritized, the mode is switched to the mode of the systems 4 and 6 where the audio signal exists, and when the audio signals exist in both systems 4 and 6, based on the level comparison. ,
Switch to transmit mode or receive mode.

As a result, in the transmission mode, the current control amplifier 18 is in the signal passing state and the current control amplifier 24 is in the signal blocking state, so that the transmission signal passing through the current controlling amplifier 18 passes through the amplifier 20 and the signal transmitting / receiving circuit 2 and the telephone line L. It is sent to the _{1, L 2.} In the reception mode, the current control amplifier 18 is in the signal cutoff state and the current control amplifier 24 is in the signal passage state. Therefore, the reception signal passing through the current control amplifier 24 is amplified by the amplifier 26 and then applied to the speaker 28. Will be played.

Therefore, it is possible to erroneously transmit or receive an unnecessary signal component such as noise by installing the transmission / reception side signal determination circuits 34 and 36 that determine such a required signal component and an unnecessary signal component. Even if there is no noise and the other party's telephone has a lot of noise components, the interruption on the transmitting side is easy to occur and the communication quality becomes good, as in the case where there is no noise.

Further, in this transmission / reception switching device, the hybrid circuit 8 of the transmission / reception systems 4 and 6 and the signal transmission / reception circuit 2 except for the handset 12 is used.
Can be configured by a one-chip semiconductor integrated circuit, the configuration can be simplified and made compact, and the reliability of transmission / reception switching can be improved.

FIG. 2 shows a concrete circuit configuration example of the transmission / reception side signal discrimination circuits 34 and 36 in the transmission / reception switching device of FIG.

In FIG. 2, an input terminal 40 formed at the non-inverting input terminal (+) of the differential amplifier 38 is applied with a signal for determining whether it is a necessary signal component or an unnecessary signal component. A feedback circuit is added to the differential amplifier 38 by a diode 42 connected between its output terminal and its inverting input terminal (-), and the differential amplifier 38 and the diode 42 constitute a logarithmic compression amplifier. There is.

The logarithmically compressed signal is applied to the base of the transistor 44, and the level shift signal extracted from the emitter of the transistor 44 is applied to the first buffer circuit 46. A first time constant circuit composed of a first capacitor 50 and a first resistor 52 is connected to the external connection terminal 48 formed on the emitter of the transistor 44. The first time constant τ _s = C ₁ · R ₁ determined by the capacitance C _{1 of the} capacitor 50 and the resistance value R _{1 of the} resistor 52 corresponds to the audio frequency which is a necessary signal component, and when the audio signal arrives. The capacitor 50 is charged to a predetermined voltage.

As a result, the charging voltage of the capacitor 50 appears at the emitter of the transistor 44, and this charging voltage is applied to the voltage dividing circuit composed of the resistors 54 and 56 through the first buffer circuit 46 and the second buffer circuit 58. Added to. A reference voltage Vref from a reference voltage source (not shown) is applied to the voltage dividing circuit of the resistors 54 and 56 through a terminal 60.

The output of the buffer circuit 58 is applied to the connection point between the resistor 64 and the capacitor 66 in the second time constant circuit including the second resistor 64 and the second capacitor 66 via the diode 62 connected in the reverse direction. At the same time, the voltage is applied to the inverting input terminal (−) of the differential amplifier 68, and the voltage based on the audio signal is applied to the non-inverting input terminal (+) of the differential amplifier 68 from the voltage dividing point of the resistors 54 and 56. Output terminal 7
The decision output 72 is taken from 0.

In the time constant circuit including the resistor 64 and the capacitor 66, the resistance value R ₂ of the resistor 64 and the capacitance C of the capacitor 66.
_{The second} time constant τ _L = C ₂ · R ₂ determined by 2 corresponds to the interval of the incoming voice signal.

The power supply voltage Vcc is applied from the power supply terminal 74 to the transistor 44 and the time constant circuit including the resistor 64 and the capacitor 66.

With such a configuration, the audio signal including the noise component applied to the input terminal 40 is logarithmically compressed via the differential amplifier 38 and the diode 42, and then applied to the base of the transistor 44.

Since the time constant of the time constant circuit composed of the capacitor 50 and the resistor 52 corresponds to the audio frequency which is a necessary signal component, the capacitor 50 is charged to a predetermined voltage while the audio frequency is maintained, That is, if the voice frequency is not present. If only noise arrives, the charging voltage is discharged through the resistor 52.

The charging voltage of the capacitor 50 is the buffer circuit 4
It is added to the resistors 54 and 56 via 6 and to the cathode of the diode 62 via the buffer circuit 58. The voltage divided by the voltage dividing circuit of the resistors 54 and 56 is applied to the non-inverting input terminal (+) and the inverting input terminal (-) of the differential amplifier 68 installed as a comparison means. It is compared with the charging voltage of the capacitor 66.

In the capacitor 66, the diode 62 is a buffer circuit 58.
When the capacitor 50 is reverse biased with the output voltage, the capacitor 50 is charged, that is, when the capacitor 50 is charged to a predetermined voltage by the arrival of the audio signal, the capacitor 50 is changed to the charged state. In other words, when the capacitor 50 is not charged to the predetermined voltage, the capacitor 66 is discharged from the inside of the buffer circuit 58 to the ground side via the diode 62.

As a result, when a voltage is applied to the non-inverting input terminal (+) of the differential amplifier 68 from the voltage dividing point of the resistors 54 and 56, the inverting input terminal (-) is always at a low level at that time, so When the output level of the dynamic amplifier 68 becomes high potential (H), the charging of the capacitor 66 progresses, and the charged voltage exceeds the voltage applied to the non-inverting input terminal (+), the output level of the differential amplifier 68 changes. It becomes a low potential (L).

Therefore, when the audio signal is present, the output terminal 7
At 0, the judgment output 72 having the time width t given by the time constant τ _L determined by the resistor 64 and the capacitor 66 is generated.

According to such a signal discriminating circuit, the voice signal has a predetermined frequency range and a specific signal interval, and the noise has a frequency range close to infinity and is generated continuously. The presence of the required signal component can be determined.

In the embodiment, the discrimination between the audio signal component and the noise has been described, but the time constants of the capacitor 50 and the resistor 52 and the time constant circuit of the resistor 64 and the capacitor 66 which configure the filter circuit, respectively. By changing, it is possible to distinguish between the necessary signal component and the unnecessary signal component.

As described above, according to the present invention, the presence or absence of a voice signal is determined by whether or not each signal passing through the transmission system and the reception system is at a predetermined level in the frequency range that the voice signal should have, The discriminative output can be used to switch between transmission and reception, and if an audio signal exists between the transmission and reception systems, transmission and reception can be switched based on the level comparison between the two, and there are unnecessary signal components such as noise components. Even if there is an interrupt, the interrupt on the transmitting side is easily generated, and transmission / reception of a necessary signal is not hindered by an unnecessary signal component such as noise, reliable transmission / reception switching can be performed, and call quality can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission / reception switching device of the present invention, and FIG. 2 is a circuit diagram showing a concrete circuit configuration example of a signal discriminating circuit on the transmitting side or the receiving side. 4 ... Transmission system, 6 ... Reception system, 14 ... Microphone, 1
8 ... Current control amplifier (transmission side signal switching circuit), 24 ... Current control amplifier (reception side signal switching circuit), 28 ... Speaker, 30 ... Comparator, 32 ... Switching control circuit, 34 ... Transmission side signal discriminating circuit, 36 ... reception side signal discrimination circuit, 38 ... differential amplifier, 42 ... diode, 44 ... transistor, 46
... first buffer circuit, 52 ... first resistance, 54, 56
... resistor (voltage dividing circuit), 58 ... second buffer circuit, 62
... diode, 64 ... second resistance, 66 ... second capacitor, 68 ... differential amplifier (comparing means), 72 ... audio signal discrimination output.

Claims (1)

[Claims] 1. A microphone for inputting a voice to be transmitted, a speaker attached to the microphone for reproducing a voice, and a transmission system for transmitting a transmission signal from the microphone to a line side. A transmission side signal switching circuit that passes or blocks, and is installed in a reception system that receives a reception signal from the line side,
A signal switching circuit on the receiving side that passes or blocks the reception signal, a comparator that compares the levels of the transmission signal and the reception signal, and generates an output that indicates the comparison result, and the transmission signal or the transmission signal from the transmission system. A signal discriminating circuit for discriminating the presence or absence of an audio signal by receiving the received signal from a receiving system, and a transmitting side signal switching circuit or a receiving side signal switching circuit depending on the comparison output of the comparator and the discrimination output of the signal discriminating circuit. In a transmission / reception switching device comprising a switching control circuit for selectively switching to a signal passing state or a signal blocking state, the signal discriminating circuit receives the transmission signal or the reception signal and responds to the transmission signal or the reception signal. And a logarithmic compression amplifier, and the output of this amplifier is added to the base to extract a signal current corresponding to the signal to be discriminated. A transistor, a first capacitor charged by the signal current through the transistor, and a first resistor for discharging the charging voltage are provided, and a first time constant corresponding to the frequency of the audio signal to be discriminated is provided. A set first time constant circuit, a voltage divider circuit to which the charging voltage of the first capacitor is applied through a first buffer circuit, and divides and extracts the charging voltage; and a second voltage source connected to a power supply. A series circuit of a resistor and a second capacitor is provided, a second time constant corresponding to the interval of the audio signal is set, and the first buffer is provided at a connection point of the second resistor and the second capacitor. The output of the circuit is the second
Of the second time constant circuit applied through the buffer circuit and the diode, and the charging voltage of the second capacitor and the DC voltage extracted by the voltage dividing circuit are compared, and an output indicating the magnitude relationship between the two is output as an audio signal. A transmission / reception switching device, comprising: a comparison unit that takes out as a determination output.