JP6781380B2 - FM receiver and wireless communication device equipped with it - Google Patents

Description

The present invention relates to an FM receiver, particularly to an FM receiver preferably used in a wireless communication device for transmitting and receiving, and the wireless communication device including the FM receiver.

In the FM transmitter / receiver, in order to improve the S / N of the demodulated signal on the receiving side, the treble range is pre-emphasis on the transmitting side and de-emphasis on the receiving side. For example, in the case of de-emphasis, the low frequency component of 300 Hz is emphasized by 10 dB as compared with the reference component of 1 kHz. As a result, flat characteristics can be obtained from the low range of 300 Hz to the high range of 3 kHz without unnecessarily increasing the degree of modulation in FM modulation, and the circuit configuration is such that voice calls can be made clearly. ..

By the way, in the case of the FM receiver, if there is no received signal, that is, if the FM radio receiver is out of tune, or if the FM radio has a large noise component of the received signal, white noise called "Za" is emitted from the speaker. I can hear it. Therefore, for example, in the case of an FM radio receiver, a mute means for muting the white noise from an RSSI signal, or in the case of a wireless communication device, from a noise or tone squelch signal, is provided in the audio signal reproduction system. .. This prevents jarring noise from being played back at high volume.

However, especially in the case of a wireless communication device that transmits and receives, there are cases where it is desired to capture a signal having a large noise component such that the squelch does not open, or in order to adjust the volume, the mute operation in the mute means is forcibly released. A release means that can be provided is provided. Therefore, if the mute operation is forcibly released while the adjustment volume (volume) is large, the white noise that was not originally pre-emphasis is output from the speaker after only de-emphasis. As a result, the components in the bass range, particularly around 300 Hz, may be emphasized, the acoustic energy may become excessive, the allowable input level of the speaker may be exceeded, and the internal wiring of the speaker may be disconnected.

On the other hand, Patent Document 1 is a receiver for FM broadcasting, and is provided with a switch for selecting whether or not to give de-emphasis characteristics in order to utilize the white noise in a detuning state. Then, when a normal broadcast signal is received, the switch is turned on to give de-emphasis characteristics, and when white noise is being output, the switch is turned off so that the de-emphasis characteristics are not given.

No. 55-133643

The above-mentioned prior art can obtain an output with de-emphasis characteristics and an output without de-emphasis characteristics, but since it is a user selection, if the selection is wrong, there is still a risk of disconnection of the speaker as described above. ..

An object of the present invention is to perform detuning or no detuning in an FM receiver in which high-frequency pre-emphasis and de-emphasis processing is performed between transmission and reception to improve the S / N of the demodulated signal on the receiving side. It is an object of the present invention to provide an FM receiver capable of preventing damage to a speaker due to white noise energy due to forced release of a mute operation at a signal, and a wireless communication device including the FM receiver.

The FM receiver of the present invention is an FM receiver in which the S / N of the demodulated signal on the receiving side is improved by performing high-frequency pre-emphasis and de-emphasis processing between transmission and reception. A mute means for causing the reproduction system to perform a mute operation by squelch or RSSI, and a circuit provided in connection with a circuit for performing the de-emphasis processing in the audio signal reproduction system and performing the de-emphasis processing. It is characterized by including an invalidation means for disabling the function and a release means for forcibly canceling the mute operation in the mute means and activating the invalidation means at the time of the forced release.

According to the above configuration, in order to improve the S / N of the demodulated signal on the receiving side, it is used for receiving the FM signal in which the treble range is pre-emphasis on the transmitting side and de-emphasis on the receiving side. In the FM receiver, the mute means for performing a mute operation by squelch or RSSI is provided in the audio signal reproduction system, and the mute means for confirming a signal having a large noise component and adjusting the volume. When a release means capable of forcibly canceling the mute operation in the above is provided, the function of the circuit that performs the de-emphasis processing is invalidated in relation to the circuit that performs the de-emphasis processing in the audio signal reproduction system. The invalidation means is provided, and the cancellation means activates the invalidation means at the time of the forced release.

For example, the invalidation means is configured to include a bypass circuit provided in parallel with a circuit that performs de-emphasis processing, and a switching means provided before and after the circuit to switch the path of the audio signal. ..

Therefore, the bass range is about to be restored to the original level by turning on the de-emphasis, for example, the bass range component of 300 Hz is emphasized by 10 dB compared to the reference component of 1 kHz, and the large adjustment volume (volume). ), If white noise due to detuning or no signal that was not originally pre-emphasis is given to the speaker, the energy in the bass range, especially around 300 Hz, is excessively input (allowable input of the speaker). There is a possibility that the internal wiring of the speaker will be broken due to (exceeding the level), but by canceling the de-emphasis by the invalidation means, such a problem can be prevented. be able to.

Further, the wireless communication device of the present invention is characterized by including the FM receiver described above and an FM transmitter performing the pre-emphasis.

According to the above configuration, unlike a radio whose transmission frequency is often known in advance, in a wireless communication device that transmits and receives, the frequency at which transmission is performed often changes from time to time.

Therefore, in the case of a wireless communication device that performs such transmission / reception, the mute operation is often forcibly canceled when confirming a signal having a large noise component or adjusting the volume, and the present invention is preferable. is there.

As described above, the FM receiver of the present invention and the wireless communication device provided with the FM receiver pre-emphasis the treble range on the transmitting side and the receiving side in order to improve the S / N of the demodulated signal on the receiving side. In the FM receiver used for receiving FM signals to be de-emphasis, a mute means for performing mute operation by squelch or RSSI is provided in the audio signal reproduction system, and a signal having a large noise component can be confirmed. , In connection with the circuit that performs the de-emphasis processing in the audio signal reproduction system when a release means capable of forcibly canceling the mute operation in the mute means is provided in order to adjust the volume. , A disabling means for disabling the function of the circuit that performs the de-emphasis processing is provided, and the disabling means activates the disabling means at the time of the forced cancellation.

Therefore, if the white noise due to detuning or no signal is applied to the speaker only by de-emphasis even though it is not originally pre-emphasis, it is low when the adjustment volume is high. There is a possibility that the internal wiring of the speaker will be disconnected due to an excessive input in the sound range, but by canceling the de-emphasis by the invalidation means, such a problem can be prevented. be able to.

It is a block diagram which shows the electrical structure of the FM receiver which concerns on one Embodiment of this invention. It is a block diagram which shows an example of the de-emphasis circuit in the FM receiver.

FIG. 1 is a block diagram showing an electrical configuration of the FM receiver 1 according to the embodiment of the present invention. The FM receiver 1 of FIG. 1 is combined with an FM transmitter (not shown) to form a wireless communication device. The FM signal received by the antenna 2 is amplified by the high frequency circuit 3 and then input to the reception detection circuit IC4 to demolish the audio signal. In the wireless communication device in which the FM receiver 1 is used, the S / N of the demodulated signal on the receiving side is improved by performing high-frequency pre-emphasis and de-emphasis processing between transmission and reception. There is. Therefore, the demodulated audio signal is applied to the low frequency amplifier 6 for amplification after the high frequency range is suppressed through the de-emphasis circuit 5, and is acoustically output from the speaker 7.

For example, the pre-emphasis and de-emphasis are performed at 6 dB / oct. In pre-emphasis, the bass component of 300 Hz is suppressed by 10 dB compared to the reference component of 1 kHz, and in de-emphasis, 10 dB is emphasized as shown in FIG. It is realized by being done. The gain (amplification degree) of the low-frequency amplifier 6 can be adjusted by the volume knob 8 which is a volume adjusting means.

Further, the demodulated audio signal from the reception detection circuit IC4 is input to the squelch detection circuit 9. For example, while the audio signal is detected by noise squelch, the low frequency amplifier power supply 10 is turned on to the low frequency amplifier 6. The audio signal is amplified, the low frequency amplifier power supply 10 is turned off while the audio signal is not detected, and a mute operation is performed so that unpleasant white noise is not output from the speaker 7. The squelch detection circuit 9, the low frequency amplifier power supply 10, and the low frequency amplifier 6 constitute a mute means. The squelch is not limited to noise, and may be performed in response to a tone signal or the like, or in the case of an FM radio receiver, it may be performed from the received signal strength (RSSI). Further, the mute operation may also be performed by an arbitrary method in the audio signal reproduction system, such as cutting the input audio signal to the low frequency amplifier 6.

The FM receiver 1 configured as described above is provided with a forced squelch switch 11. The forced squelch switch 11 forcibly turns on the low-frequency amplifier power supply 10 even if the squelch detection circuit 9 does not detect an audio signal in the FM receiver 1 of the wireless communication device capable of transmitting and receiving. This is a release means capable of forcibly canceling the mute operation in the mute means. This makes it possible for the user to play back the audio signal even in the state of white noise in order to check the signal with a large noise component (search for a station calling far away) and adjust the volume. There is.

However, in that case, if white noise due to detuning or no signal is given to the speaker 7 in a state where the volume 8 has a large adjustment volume, the white noise that is not originally pre-emphasis becomes the de-emphasis circuit. In No. 5, only de-emphasis is performed and the speaker 7 outputs the output. As a result, the bass region, particularly the components around the 300 Hz, are emphasized, the acoustic energy becomes excessive, and the allowable input level of the speaker 7 is increased. There is a risk that the internal wiring of the speaker 7 will be broken. Further, since the radio wave condition is not always constant, the detection output may suddenly increase from the state where the weak radio wave is received, and in this case as well, there is a risk of disconnection of the speaker 7.

Therefore, in the present embodiment, a bypass circuit 12 is provided in parallel with the de-emphasis circuit 5, and switching means 13 and 14 for switching the path of the audio signal are provided before and after the circuit. The switching means 13 and 14 are switched and controlled by the forced squelch switch 11, and while the forced squelch switch 11 is turned on, an audio signal is input to the low frequency amplifier 6 through the bypass circuit 12 and turned off. The audio signal is input to the low frequency amplifier 6 through the de-enhancement circuit 5.

The bypass circuit 12 and the switching means 13 and 14 are provided in connection with the de-emphasis circuit 5, constitute an invalidation means for disabling the function of the de-emphasis circuit 5, and are forced squelch switches which are the release means. It will be activated by 11.

The invalidation of the function of the de-enhancement circuit 5 is realized by, for example, as shown in FIG. 2, the de-enhancement circuit 5 is a high-frequency cut capacitor 53 ground-faulting the line 52 of the audio signal provided with the limiting resistor 51. In this case, it may be appropriately realized according to the configuration of the audio signal reproduction system, such as providing a switch 54 for separating the high frequency cut capacitor 53 from the audio signal line 52 by turning on the forced squelch switch 11.

With this configuration, in the FM receiver 1 of the present embodiment, when the low frequency amplifier power supply 10 is turned on by the forced squelch switch 11 regardless of the detection result of the squelch detection circuit 9, the audio signal is displayed. Since it does not pass through the emphasis circuit 5 but passes through the bypass circuit 12, even if white noise that is not originally pre-emphasis is input while the adjustment volume of the volume 8 is high, the low frequency component can be suppressed as a result. This makes it possible to protect the speaker 7 from excessive input and prevent problems such as disconnection.

Further, the FM receiver 1 of the present embodiment is used for a wireless communication device, which is different from a radio whose transmission frequency is often known in advance, and which frequency is often transmitted depending on the occasion. Be done. Therefore, in the case of the wireless communication device that transmits and receives, the mute operation is often forcibly released when a signal having a large noise component is confirmed or the volume is adjusted, and the present invention is suitable.

Furthermore, in the FM receiver 1 of the present embodiment, the squelch detection circuit 9 lowers the gain of the low-frequency amplifier 6 interposed between the de-enhancement circuit 5 and the speaker 7, specifically, the low-frequency amplifier power supply. Since the mute operation is performed by turning off 10, the mute operation can be realized with a normal volume adjustment configuration without interposing a special configuration such as a switch in the audio signal reproduction system.

1 FM receiver 2 antenna 3 high frequency circuit 4 reception detection circuit IC
5 Deenfasis circuit 6 Low frequency amplifier 7 Speaker 8 Volume knob 9 Squelch detection circuit 10 Low frequency amplifier power supply 11 Forced squelch switch 12 Bypass circuit 13, 14 Switching means

Claims (3)

In an FM receiver that improves the S / N of the demodulated signal on the receiving side by performing high-frequency pre-emphasis and de-emphasis processing between transmission and reception.
A mute means for causing the audio signal reproduction system to perform a mute operation by squelch or RSSI,
In the audio signal reproduction system, an invalidation means provided in connection with the circuit that performs the de-emphasis processing and invalidating the function of the circuit that performs the de-emphasis processing.
An FM receiver characterized in that the mute operation in the mute means is forcibly released, and at the time of the forcible release, the release means for activating the invalidation means is included. The disabling means is configured to include a bypass circuit provided in parallel with the circuit that performs the de-emphasis processing, and a switching means provided before and after the circuit to switch the path of the audio signal. The FM receiver according to claim 1. A wireless communication device including the FM receiver according to claim 1 or 2 and an FM transmitter that performs the pre-emphasis.

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