JP3780169B2 - Voice squelch circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a voice squelch function used for a wireless receiver, and more particularly to a technique for realizing the voice squelch function without using a complicated analog circuit.
[0002]
[Prior art]
Conventionally, in a radio receiver, demodulation is performed when the level of the received signal becomes low in order to prevent the dominant noise component from being output as a demodulated signal to the subsequent stage as the level of the received signal decreases. A squelch circuit that cuts off or suppresses output to the subsequent stage of the signal is generally used.
In such a squelch circuit, when the level of the received signal is detected and the detected level falls below a preset threshold value, the squelch gate means provided in the subsequent low-frequency circuit is A configuration is adopted that closes and blocks or suppresses output to the subsequent stage. (The case where the level of the carrier wave is detected and used as the level of the received signal is called S meter squelch, and the case where the level of the noise component in the demodulated signal is detected and used as the level of the received signal is called noise squelch.)
[0003]
In addition, a wireless receiver provided with a scanning function for searching only a frequency where a reception signal exists by automatically scanning the reception frequency and stopping the scan at a frequency when the squelch gate means is opened is also conventionally used. Generally present.
However, the conventional squelch circuit as described above performs open / close control of the squelch gate means by detecting only the level of the received signal, and does not determine whether the demodulated signal is an audio signal. . For this reason, no countermeasure is taken against signals having frequency components included in the frequency band of the audio signal, for example, interference and interference signals such as telegraph waves and FSK signal waves. In this case, squelch The gate means is not closed, and the demodulated signal (in this case, the demodulated signal becomes a highly periodic tone signal) is output to the subsequent stage as it is.
[0004]
In addition, in a wireless receiver provided with a scanning function as described above, scanning can be stopped by interference such as telegraph waves or interference signals, and only a frequency where an audio signal exists can be searched well. Can not.
In view of such problems, it is determined whether or not the demodulated signal is an audio signal, and the squelch gate means is closed when the demodulated signal is not an audio signal even if the level of the received signal is equal to or higher than a threshold value. Can be solved. Such a squelch function is called a voice squelch function.
In order to realize such an audio squelch function, it is necessary to determine whether or not the demodulated signal is an audio signal. In this case, it is determined whether or not the demodulated signal is a tone signal with strong periodicity, and if it is a tone signal, it is determined that it is not a voice signal.
[0005]
Then, when the signal is an audio signal, the squelch gate means may be opened, and when the signal is not an audio signal, the squelch gate means may be closed.
An example of such an audio squelch circuit will be described with reference to FIG.
In FIG.
The demodulated output of the receiving circuit 101 is passed through the limiter amplifier 102 to suppress the amplitude component and input to the one-shot multi 103.
The one-shot multi 103 generates an output pulse with a constant width at the timing when the input signal crosses the zero point from minus to plus. Therefore, the density of the output pulse changes in proportion to the frequency of the input signal.
The output pulse is input to the low-pass filter 104 and smoothed to obtain a DC voltage proportional to the frequency of the input signal.
[0006]
The output of the low-pass filter 104 is input to a comparator 105 having hysteresis characteristics, and if the amount of change in the DC voltage is equal to or greater than a predetermined threshold value, the frequency of the input signal changes, It is determined that there is a voice squelch control signal that opens the voice squelch, and if the change amount of the DC voltage is less than a predetermined threshold value, the input signal is determined to be a tone signal, An audio squelch control signal for closing the squelch is output.
When the voice squelch is opened by controlling the squelch gate means 110 arranged on the line of the received signal by the voice squelch control signal outputted in this way, the inputted received signal is sent to the low frequency circuit at the subsequent stage. In the case of outputting and closing the audio squelch, control is performed so that the input reception signal is suppressed and output to the low-frequency circuit at the subsequent stage.
The above voice squelch is used in combination with noise squelch or the like.
[0007]
[Problems to be solved by the invention]
However, the above-described voice squelch has a problem in that the number of parts is increased and the circuit is complicated in order to realize the above functions with an analog circuit configuration.
In addition, since it takes time for the one-shot multi or low-pass filter to operate, there is a problem that the reaction time becomes long and the squelch operation is delayed.
In addition, there is a problem that trial adjustment of circuit constants (threshold values and time constants) of each part in each circuit configuration is necessary.
[0008]
Therefore, the present invention has been made for the purpose of realizing an audio squelch circuit that has a short reaction time by digital processing and does not require adjustment of circuit constants.
[0009]
[Means for Solving the Problems]
In claim 1 of the voice squelch circuit according to the present invention,
Reception level detection means for detecting the level of the reception signal and outputting a comparison result with a first threshold value set in advance ;
Notch filtering means configured to remove a signal component with strong periodicity included in the demodulated signal and output a filter output signal;
Audio level detection means for detecting the level of the filter output signal and outputting a comparison result with a preset second threshold value ;
Only when the level of the received signal is greater than the first threshold and the level of the filter output signal is greater than the second threshold, the squelch gate is opened and the input demodulated signal is passed. And squelch gate means for outputting to the subsequent stage .
In claim 2,
Reception level detection means for detecting the level of the reception signal and outputting a comparison result with a first threshold value set in advance;
Notch filtering means configured to remove a signal component with strong periodicity included in the demodulated signal and output a filter output signal;
Audio level detection means for detecting the level of the filter output signal and outputting a comparison result with a preset second threshold value;
Only when the level of the received signal is greater than the first threshold and the level of the filter output signal is greater than the second threshold, the squelch gate is opened and output from the notch filtering means. Squelch gate means for passing the signal and outputting it to the subsequent stage.
In claim 3 ,
The notch filtering means
Delay means for delaying the demodulated signal;
A filter that receives a delayed demodulated signal and selectively outputs a signal component having a strong periodicity based on characteristics determined by a set coefficient;
An arithmetic means for subtracting the output signal of the filter from the demodulated signal to remove a signal component having a strong periodicity and outputting a filter output signal;
And an adaptive algorithm for setting the coefficient of the filter based on the filter output signal.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, a voice squelch circuit according to the present invention will be described in detail based on the drawings showing embodiments thereof.
[0011]
FIG. 1 is a block diagram of a receiving apparatus employing an audio squelch circuit according to the first embodiment of the present invention.
In FIG.
1 is a receiving device, 2 is a receiving circuit that amplifies and demodulates a received signal received via an antenna and outputs a demodulated signal, 3 is an audio squelch circuit that suppresses output to the subsequent stage of the demodulated signal, and 4 is an audio squelch circuit Reference numeral 5 denotes a low-frequency amplifier circuit that amplifies the demodulated signal that has passed through 3, and a speaker that outputs the amplified low-frequency signal as an acoustic signal.
The voice squelch circuit 3 detects the level of the received signal by detecting the level of the carrier component, and outputs a result of comparison with a first threshold value set in advance, and a demodulated signal Is input, the notch filtering means 31 for removing signal components with strong periodicity, and the level of the filter output signal output from the notch filtering means 31 is detected and compared with a preset second threshold value. Based on the sound level detection means 32 for outputting the result, and the output of the sound level detection means 32 and the output of the reception level detection means 6, the input demodulated signal passes (squelch open) / suppresses (squelch close). Squelch gate means 33 for controlling Note that the suppression state of the demodulated signal includes a state where the demodulated signal is completely blocked. Further, the reception level detection means 6 may detect the level of the reception signal by detecting the level of the noise component included in the demodulated signal.
[0012]
The notch filtering means 31 is a notch filter composed of an adaptive filter by a known DSP process. In FIG. 3, an input demodulated signal is input to a filter 311 whose characteristics are determined by a set coefficient via a delay means 314. The arithmetic means 312 outputs an error signal obtained by subtracting the output signal of the filter 311 from the input demodulated signal. The error signal is output as a filter output signal to the sound level detection means 32 and also to the adaptive algorithm means 313. The adaptive algorithm means 313 sets the coefficient of the filter 311 based on the input error signal. Here, the adaptive algorithm 313 is programmed in advance so that the filter 311 sets a coefficient that passes only a tone signal component having a strong periodicity. As a result, the filter output signal is a signal obtained by removing only the tone signal component from the demodulated signal.
[0013]
The squelch gate means 33 passes an input demodulated signal only when the level of the received signal is higher than the first threshold and the level of the filter output signal is higher than the second threshold ( It is controlled to open the squelch.
The sound level detection means 32 may be realized by an analog circuit, but may be realized by the same DSP processing as the notch filtering means 31 or by a microcomputer unit having a built-in A / D conversion means. Also good.
[0014]
In the above configuration, when the level of the reception signal detected by the reception level detection unit 6 is smaller than the first threshold value, the squelch gate unit 33 is controlled to suppress (squelch close) the demodulated signal. This prevents the dominant noise component from being output to the low-frequency amplifier circuit 4 as a demodulated signal when no signal is received by the receiving circuit 2 or when a weak signal is received. Is done.
On the other hand, when the level of the reception signal detected by the reception level detection means 6 is higher than the first threshold value, the reception circuit 2 is receiving some signal, so that the noise component in the demodulated signal The demodulated signal is dominated by the demodulated component of the received signal. However, when the received signal is an interference signal such as a telegraph wave or an interference signal, the demodulated signal becomes an unintended tone signal. Therefore, the notch filtering unit 31 removes the tone signal component from the demodulated signal, and the level of the output signal is detected by the audio level detecting unit 32. That is, when the received signal is an interference signal such as a telegraph wave or an interference signal, the tone signal, which is the dominant demodulating component, is removed by the notch filtering means 31, so that the level of the demodulated signal decreases, and the second Smaller than the threshold value. Therefore, the squelch gate means 33 is controlled so as to suppress (squelch close) the demodulated signal, and the tone signal is prevented from being output to the low frequency amplifier circuit 4 as the demodulated signal. On the other hand, when the received signal is the target signal, the demodulated signal is an audio signal, so that the level is reduced in the notch filtering means 31 from which only a signal component having a strong periodicity such as a tone signal is removed. Instead, the demodulated signal level is greater than the second threshold. Therefore, the squelch gate means 33 is controlled so that the demodulated signal passes (squelch open), and the audio signal is output to the low frequency amplifier circuit 4 as it is as a demodulated signal.
[0015]
In this way, even when a received signal exists, if the demodulated component is a tone signal, the demodulated signal is output only to the demodulated signal without outputting the demodulated signal to the subsequent stage. The voice squelch function for outputting to the subsequent stage is realized. Further, in a receiving device provided with a scanning function, scanning is not stopped by interference such as telegraph waves or interference signals, and only a frequency where an audio signal exists can be searched well.
[0016]
FIG. 2 is a block diagram of a second embodiment that realizes a function of removing a tone signal mixed in a demodulated signal in addition to the voice squelch function. In the first embodiment described above, when an audio signal and a tone signal are mixed in the demodulated signal, the demodulated signal is output to the subsequent stage as it is. In the present embodiment, Is effective in such a case.
[0017]
In FIG. 2, 21 is a receiving device, 22 is a receiving circuit that amplifies and demodulates a received signal received via an antenna and outputs a demodulated signal, 23 is an audio squelch circuit that suppresses output to the subsequent stage of the demodulated signal, 24 Is a low-frequency amplifier circuit that amplifies the demodulated signal that has passed through the audio squelch circuit 23, and 25 is a speaker that outputs the amplified low-frequency signal as an acoustic signal.
[0018]
The audio squelch circuit 23 detects the level of the received signal by detecting the level of the carrier wave component, and outputs a comparison result with a first threshold value set in advance, and a demodulated signal And a notch filtering unit 231 that removes a signal component with strong periodicity, and a level of a filter output signal output from the notch filtering unit 231 is detected and compared with a preset second threshold value. Based on the sound level detection means 232 for outputting the result, and the output of the sound level detection means 232 and the output of the reception level detection means 26, the filter output signal to be input is passed (squelch open) / suppressed (squelch closed). ) Squelch gate means 233 for controlling. The suppression state of the filter output signal includes a state where the filter output signal is completely blocked. Further, the reception level detection means 26 may detect the level of the reception signal by detecting the level of the noise component included in the demodulated signal. The structure and operation of each configuration are the same as those in the first embodiment.
[0019]
In the above configuration, when the target signal and interference such as a telegraph wave or interference signal are mixed in the received signal, the demodulated signal is a signal in which an audio signal and a tone signal are mixed. In this case, since the audio signal is included in the demodulated signal, the audio level detection means 232 detects a signal larger than the second threshold value, and the squelch gate means 233 is opened. However, in the present embodiment, the signal passing through the squelch gate means 233 is not the demodulated signal as it is, but the filter output signal that has passed through the notch filtering means 231. Only the signal from which only the tone signal is removed from the signal, that is, the audio signal is output.
[0020]
In this way, even when the audio signal and the tone signal are mixed in the demodulated signal, only the audio signal can be output to the subsequent stage.
[0021]
【The invention's effect】
According to the voice squelch circuit of the present invention, the notch filtering means by the DSP processing is provided to detect the presence or absence of a signal component having a strong periodicity such as a tone signal and the presence or absence of a signal component having a strong periodicity such as a tone signal. Since the squelch gate means is controlled in accordance with the received signal level, a voice squelch circuit that has a short reaction time and does not require adjustment of circuit constants can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram of a first embodiment of an audio squelch circuit according to the present invention.
FIG. 2 is a block diagram of an audio squelch circuit according to a second embodiment.
FIG. 3 is a block diagram of a configuration example of notch filtering means used in the voice squelch circuit.
FIG. 4 is a block diagram of a conventional audio squelch circuit.
[Explanation of symbols]
1, 21 Reception device 2, 22 Reception circuit 3, 23 Audio squelch circuit 4, 24 Low frequency amplifier circuit 5, 25 Speaker 6, 26 Reception level detection means 31, 231 Notch filtering means 32, 232 Audio level detection means 33, 233 Squelch gate means 311 Filter 312 Operation means 313 Adaptive algorithm
314 Delay means

Claims (3)

Reception level detection means for detecting the level of the reception signal and outputting a comparison result with a first threshold value set in advance ;
Notch filtering means configured to remove a signal component with strong periodicity included in the demodulated signal and output a filter output signal;
Audio level detection means for detecting the level of the filter output signal and outputting a comparison result with a preset second threshold value ;
Only when the level of the received signal is greater than the first threshold and the level of the filter output signal is greater than the second threshold, the squelch gate is opened and the input demodulated signal is passed. And a squelch gate means for outputting to a subsequent stage . Reception level detection means for detecting the level of the reception signal and outputting a comparison result with a first threshold value set in advance;
Notch filtering means configured to remove a signal component with strong periodicity included in the demodulated signal and output a filter output signal;
Audio level detection means for detecting the level of the filter output signal and outputting a comparison result with a preset second threshold value;
Only when the level of the received signal is greater than the first threshold and the level of the filter output signal is greater than the second threshold, the squelch gate is opened and output from the notch filtering means. A voice squelch circuit comprising squelch gate means for passing a signal and outputting the signal to a subsequent stage. The notch filtering means
Delay means for delaying the demodulated signal;
A filter that receives a delayed demodulated signal and selectively outputs a signal component having a strong periodicity based on characteristics determined by a set coefficient;
An arithmetic means for subtracting the output signal of the filter from the demodulated signal to remove a signal component having a strong periodicity and outputting a filter output signal;
The speech squelch circuit according to claim 1, further comprising: an adaptive algorithm that sets a coefficient of the filter based on the filter output signal.

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