JPS6326122A - Noise squelch circuit - Google Patents

Abstract

PURPOSE:To detect a pulse noise component with narrow width by using a detector so as to detect an output of a noise amplifier in a demodulated voice circuit of a receiver via a sample-and-hold circuit. CONSTITUTION:A demodulated voice of a receiver inputted from a demodulated voice input terminal 10 is amplified by a noise amplifier 1, the amplified noise is subject to sample-and-bold processing by a sample-and-hold circuit 2, and its sample-and-hold output is detected by a detector 3. That is, in inserting the sample-and-hold circuit 2 to the output of the noise amplifier 1, the noise is converted into a pulse train having a pulse width depending on a period T of the sample-and-hold circuit 2. In making the period T of the sample-and- hold circuit 2 constant, a sufficiently strong correlation between a mean value of an output noise level of demodulated voice and a mean value of an output level of the output of the sample-and-hold circuit is obtained after a sufficiently many number of times of sample-and-hold processings. Thus, in detecting the output of the sample-and-hold circuit 2, the noise level is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise squelch circuit used in a receiver.

[Conventional technology]

Conventionally, this type of noise squelch circuit amplifies noise in a demodulation audio circuit of a receiver, and directly detects and outputs the amplified output using a wave detector.

[Problem that the invention seeks to solve]

The conventional noise squelch circuit described above obtains a stable detection output when the noise level is high or when the frequency component of the noise is low. However, if the noise waveform of demodulated audio is a narrow pulse-like waveform, even if rectified detection is performed using a detector after amplification, it will not be possible to obtain a sufficient DC level for the detection output because the pulse width is originally narrow. Ta. In addition, when using a double-wave rectifier that can obtain twice as much DC component as a half-wave rectifier as a detector circuit, for example, the point of change in the phase of pulse-like noise is delayed due to operating speed constraints of the rectifier circuit. Therefore, there was a problem that a sufficient DC level of the component could not be obtained for the detector output.

An object of the present invention is to provide a noise squelch circuit that can solve such problems and obtain a stable detection output.

[Means for solving problems]

The noise squelch circuit of the present invention includes a noise amplifier that amplifies noise in the demodulated audio output from the receiver, a sample hold circuit that holds the output of the noise amplifier at a predetermined period, and a detector that detects the output of the sample hold circuit. It consists of a container.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.6 In this embodiment, demodulated audio from a receiver inputted from an input terminal 10 is amplified by a noise amplifier 1, and a sample-hold circuit is applied to the amplified noise. 2 performs sample and hold, and the sample and hold output is detected by a detector 3. That is, when the sample-and-hold circuit 2 is inserted into the output of the noise amplifier 1 shown in FIG. 2(a), it is converted into a pulse train with a pulse width determined by the period T of the sample-and-hold circuit 2, as shown in FIG. 2(b). You can.

If the period T of this sample and hold circuit 2 is kept constant,
After a sufficiently large number of samples and holds, a sufficiently strong correlation is obtained between the average value of the output noise level of the demodulated audio and the average value of the output level of the sample and hold circuit output. Therefore, by detecting the output of the sample and hold circuit 2, the noise level can be detected. Furthermore, if the sample-and-hold period T is made sufficiently larger than the operating speed of the rectifying detector 3, a double-wave rectifier circuit or the like may be used.

Figure 3 shows a case where a switched capacitor circuit is used as an example of the circuit in Figure 1 (hereinafter abbreviated as SC). Mochi, 3
It is composed of stage operational amplifiers 21 to 23, a transistor M1, and a smoothing capacitor C6.

The block consisting of the operational amplifier 21, capacitors C1 and C2, and a switch is an SC anti-phase amplifier, and its gain G is determined by the ratio of capacitors C1 and 02 (G=C1
/C2),'. Since the output of this SC anti-phase amplifier is an SC circuit, the clock φ1. Sample and hold is performed with a period of φ2. Next, the block consisting of the operational amplifier 22, 23, capacitors 03 to C5, and switches is an SC double-wave rectifier, and its slope is −C
4/C1, and C4/CI, and the capacitor C5
corresponds to 2C3.

〔Effect of the invention〕

As explained above, the present invention makes it possible to detect narrow pulse-like noise components by detecting the output of the noise amplifier in the demodulation audio circuit of the receiver with a detector via a sample and hold circuit. There is an effect.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2(a)
, (b) are waveform diagrams showing the input and sample-and-hold outputs of FIG. 1, and FIG. 3 is a circuit diagram using an SC circuit as a specific example of FIG. 1. DESCRIPTION OF SYMBOLS 1... Noise amplifier, 2... Sample hold circuit, 3... Detector, 10... Input terminal, 11... Output terminal, 21-23... Operational amplifier. Figure 1 Figure 2

Claims (1)

[Claims] A noise squelch circuit includes a noise amplifier that amplifies noise in demodulated audio output from a receiver, a sample hold circuit that holds the output of the noise amplifier at a predetermined period, and a detector that detects the output of the sample hold circuit.