JPS5952926A - Noise suppressing circuit of receiver - Google Patents

Abstract

PURPOSE:To form a noise suppressing circuit of a receiver which does not generate squelch tail noise, by inserting a delaying circuit for delaying and outputting a demodulated output, in a period corresponding to a rise operating time of a squelch circuit. CONSTITUTION:A sound signal demodulated and outputted from a frequency discriminator 5 is delayed by a time set in advance by a delaying circuit 13, and is inputted to a voice frequency amplifier 6. On the other hand, a squelch circuit converts the demodulated output of the frequency discriminator 5 to a direct current corresponding to its noise level through a noise band filter 8, a noise amplifier 9 and a rectifier 10, and controls on-and-off operations of the voice frequency amplifier 6 by this DC signal. In this case, when a delay time of the delaying circuit 13 is made longer than a delay time peculiar to the squelch circuit, the voice frequency amplifier 6 can be turned off when squelch noise in case of the end of a call is still passing through the delaying circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver having a squelch circuit, and more particularly to a noise suppression circuit for suppressing noise generated when the squelch is cut off.

A conventional receiver of this type is the one shown in FIG. In the figure, C (1) is a high frequency amplifier, (2) is a mixer,
(3) is a mixer (a 20-band P-wave device that passes the intermediate frequency signal that is output after conversion, (4) is an intermediate-frequency amplifier), these band-pass wave devices (3), and an intermediate frequency signal. The frequency amplifiers (4) are cascaded in two stages.

(5) is a frequency discriminator, (6) is an audio frequency amplifier, (7
) is a local oscillator that injects the local signal into the mixer (2), (
8) is a noise band filter, (9) is a noise amplifier, Oo is a rectifier, and (8) to (11) constitute a squelch circuit.
[Yes, 0υ is frequency modulation (FM) or phase modulation (
A high frequency input terminal to which the received radio waves (PM) are manually input, (
04 is the audio frequency output terminal, and the above (υ~04) constitutes a receiver.

Next, the operation will be explained. The weak radio waves input from the high frequency input terminal θV are amplified by the high frequency amplifier (1) and input to the mixer (2). Here, the local oscillator (7)'s local oscillator (m) converts the signal to an intermediate frequency, the intermediate frequency band filter (third filter) attenuates unnecessary waves, and the intermediate frequency amplifier (4) further amplifies the signal. After repeating the amplification operation twice, this middle frequency radio wave is input to the frequency discriminator (5).Here, it is demodulated to the audio frequency.
The audio signal ('') is amplified to a required level by the audio frequency amplifier (6) and output from the audio frequency output terminal.

On the other hand, the noise band? /' The noise component filtered by the armpit (8) is amplified by the noise amplifier (9), and the amplified output is converted into DC by the rectifier θQ. Then, C1 controls the ON and OFF operations of the audio frequency amplifier (6) using this DC signal (that is, the squelch control signal), and amplifies and outputs the demodulated audio signal only when receiving radio waves, and prevents disconnection or separation of input radio waves. The noise during timing is caused by a squelch operation that does not output any output.

The squelch circuit of a conventional receiver is configured as described above, so when a breathtalk call ends and the received radio wave suddenly cuts out, the squelch circuit detects noise and turns off the audio frequency amplifier. The darkness of the time it takes to
However, there was a point where a momentary buzzing noise (also known as squelch tail noise) was output when a call ended.

This invention was made in order to eliminate the input point of the conventional system as described above, and by inserting a delay circuit that delays output of the demodulated output for a period corresponding to the rise operation time of the squelch circuit, the squelch・The objective is to provide a receiver noise suppression circuit that does not generate tail noise.
There is.

An embodiment of the present invention will be described above with reference to FIG.

In FIG. 2, numbers c and M (1) to (6) are the same as in the conventional case. The head is a delay circuit inserted between the frequency discriminator (5) and the audio frequency amplifier (6), and this delay time is determined by the squelch circuit using noise (C1 normal squelch 17.
The time required for outputting the control signal (the so-called operation rise time) is set to 1.

In the 21st meat, the operation up to the frequency discriminator (5) is as follows:
The month is the same as in the previous case. The audio signal demodulated and output from the frequency discrimination path (5) is delayed by a preset time by the delay circuit a4, and then sent to the audio frequency amplifier (6).
is man-powered. On the other hand, the squelch circuit uses a frequency discriminator (
Similar to the conventional one, the output of the 5th output is converted to direct current according to the level of death,
This blood flow signal 'I5' turns on the audio frequency amplifier (6).
and controls the OFF operation.

By making the delay time of this delay circuit o4 longer than the delay time unique to the squelch circuit, the squelch tail sound at the end of a call can be transmitted to the audio frequency amplifier (6) while still passing through the delay circuit o4. OFF l Rubbing (preventing squelch tail noise from coming out to the audio frequency output terminal)
becomes possible. However, since the sexual signal for telephone calls also produces a delayed IL that is determined by the delay circuit 4, if it is lengthened unnecessarily, it will become difficult to hear, which is not desirable.
For example, it is preferable to set the optimum delay time to a time corresponding to the rise operation time of the squelch circuit.

In the above embodiment, we talked about the 4U modulation (or frequency modulation) type receiver, but in general, the entire °C can be used for circuits that generate noise for a certain period of time immediately after the signal output. .

As described above, the first aspect of the present invention is that the demodulated output is delayed by a time corresponding to the start-up time of the squelch circuit and then output to the low frequency amplifier circuit, thereby preventing squelch tail miscellaneous effects from occurring. There is an effect that can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a conventional reception system, and FIG. 2 is a system diagram of an embodiment of the present invention (system termination of m machines. (5)...frequency discrimination path, (6 )...Audio frequency amplifier, (8)...External sound band P-wave device, (9)...External sound amplifier, (11...Rectifier, 0...Delay circuit. In addition, the same parts in the figure The code is the same or (indicates the target part. Agent: Kuzu Feng and others −

Claims (1)

[Claims] A receiver that receives and demodulates an input Yd wave, and amplifies and outputs the demodulated output using a low frequency amplifier, detects the noise level of the demodulated output, and operates the low frequency amplifier according to this detection level. and a delay circuit for delaying the demodulated output and inputting it to the low frequency amplifier for a time corresponding to the rise operation time of the squelch circuit. Noise suppression circuit.