JPH04293318A - Squelch circuit - Google Patents

Abstract

PURPOSE:To uniformize the performance of a circuit by means of full digital processing, to miniaturize the circuit and to reduce the current consumption. CONSTITUTION:A voice input signal through a low pass filter 1 is coded by a coding circuit 2 and the result is outputted to a noise detection circuit 3 as a branching output. The noise detection circuit 3 detects the noise and when the level exceeds a prescribed level, a word addition circuit 4 adds an exclusive word representing noise detection to its input and the result is outputted. A word detection circuit 5 detects the exclusive word and when the circuit 5 detects the word, a multi-in/off circuit 6 controls a signal input/interruption circuit 7 to interrupt the transmission of a coded signal to a next-stage. A word cancel circuit 8 eliminates the word added to the coded voice signal and outputs the result to a coded voice processing circuit 9, in which the signal is converted into an analog signal, and it is outputted via the low pass filter 10 and a low frequency amplifier 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a squelch circuit, and more particularly to a squelch circuit used in the field of wireless communications.

0002

2. Description of the Related Art A conventional squelch circuit includes a low-pass filter 12 that cuts off unnecessary high frequencies of an audio input signal, as shown in FIG.
a bandpass filter 13 whose center frequency is arbitrarily set to detect noise components included in the audio input signal; and a squelch on/off circuit 14 that controls on/off of the audio input signal depending on the magnitude of the detected noise component. , an electronic switch 15 that turns on/off signal output according to the output of the squelch on/off circuit 14 , and an audio amplifier 16 .

Next, the operation of the conventional squelch circuit will be explained.

[0004] The audio input signal output from the low-pass filter 1 is branched and output to a bandpass filter 13 .

[0005] In the demodulated voice input signal in wireless communication, the noise component of the demodulated signal is suppressed by the voice when the high-frequency signal is being received, and the power of the noise component is reduced, but the power of the demodulated signal when the high-frequency signal is not received is only the noise component. Therefore, the power of the noise component increases. In the conventional technology, the squelch on/off circuit 14 is operated depending on the magnitude of this noise component, and the electronic switch 4 is turned on/off.

[0006]

Since conventional squelch circuits use many analog electronic components, they have the disadvantage that it is difficult to equalize performance, downsize the circuit, and reduce current consumption.

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a squelch circuit that significantly facilitates uniformity of performance, miniaturization of the circuit, and reduction of current consumption by digitizing an audio input signal and performing a squelch operation. Our goal is to provide the following.

[0008]

[Means for Solving the Problems] The squelch circuit of the present invention includes an encoding means for encoding an input audio signal, and a signal outside the audio signal band included in the output of the encoding means is detected as noise and a detection level is set. noise detection means for outputting a noise detection signal when the noise detection signal exceeds a predetermined decision threshold value; Output signal on/off means for inputting the output of the word addition means and turning off or on the output of the word addition means depending on whether or not the dedicated word is detected; and an output of the output signal on/off means. and coded-speech converting means for removing the dedicated word and converting the coded speech into analog speech.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

The embodiment shown in FIG. 1 includes a low-pass filter 1 and an encoding circuit 2 constituting encoding means, a noise detection circuit 3 as a noise detection stage, a word addition circuit 4 as word addition means, A word detection circuit 5, a squelch on/off circuit 6, and a signal input/off circuit 7 constituting the output signal on/off means, an encoding/voicing circuit 9, a low-pass filter 10, and a low frequency amplifier constituting the encoding/voicing means. 11.

Next, the operation of this embodiment will be explained.

In FIG. 1, an audio input signal is input to a low-pass filter 1 to limit unnecessary high frequencies. The high band limited audio input signal is input to the encoding circuit 2 and converted into an encoded digital audio signal.

The noise component of the encoded audio signal output from the encoding circuit 2 is detected by the noise detection circuit 3.
Since noise components exist outside the audio band, the noise detection circuit 3 only needs to detect signals with frequencies outside the audio band, and targets the frequency range outside the audio band of the pass frequency of the low-pass filter 1. The average level should be taken as .

When it is determined that the noise detected by the noise detection circuit 3 exceeds a predetermined decision threshold value, a noise detection signal is outputted and inputted to the word addition circuit 4.

The word adding circuit 4 adds a special word to the encoded audio input signal to specify that noise has been detected.

When the word detection circuit 5 detects the word added by the word addition circuit 4, it outputs a word detection signal to control the squelch on/off circuit 6, and the squelch on/off circuit 6 outputs an on/off signal. Signal on/off circuit 7
is supplied to turn on/off the signal to the next stage.

The word cancel circuit 8 removes the word added by the word addition circuit 4, and then the additional voice conversion circuit 9 converts the input encoded voice into analog voice and outputs it.

The signal output from the encoder/speech converter 9 is band-limited by a low-pass filter 10, amplified to a specified level by a low-frequency amplifier 11, and then output.

The above is the operation of the present invention, and the squelch circuit, especially the noise squelch circuit, focuses on the fact that the noise level decreases when radio waves are received during wireless communication, and that the noise level increases as the reception level decreases. The processing is the same as in the conventional example.

Such a squelch circuit can be fully digitalized, which allows for uniform performance, miniaturization of the circuit by increasing the degree of device integration, and reduction of current consumption by using MOS logic.

[0022]

[Effects of the Invention] As explained above, according to the present invention, by making the squelch circuit fully digital, the performance can be made uniform, the circuit can be made smaller by increasing the degree of integration of the device, and MOS logic can be used. This has the effect that it is possible to reduce current consumption.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a conventional squelch circuit.

[Explanation of symbols]

1 Low-pass filter 2 Encoding circuit 3 Noise detection circuit 4 Word addition circuit 5 Word detection circuit 6 Squelchion/off circuit 7 Signal on/off circuit 8 Word cancel circuit 9 Coding/voicing circuit 10 Low-pass filter 11 Low frequency amplifier 12 Low-pass filter 13 Bandpass filter 14 Squelchion/off circuit 15 Electronic switch 16 Audio amplifier

Claims (1)

[Claims] 1. Encoding means for encoding an input audio signal, and detecting a signal outside the audio signal band included in the output of the encoding means as noise, and detecting the noise when the detection level exceeds a predetermined decision threshold value. noise detection means for outputting a signal; word addition means for receiving the noise detection signal and adding a dedicated word specifying noise detection to the output of the encoding circuit; output signal on/off means for turning off or on the output of the word adding means in response to whether or not a word is detected; 1. A squelch circuit comprising coded voice converting means for converting into analog voice.