JPH0832468A - Squelch circuit - Google Patents

Abstract

PURPOSE:To execute a proper squelch operation by setting automatic answering telephone set a proper squelch setting voltage corresponding to a change in a level of a received signal. CONSTITUTION:A gain of a receiver 2 is controlled based on an AGC voltage Vs generated by an AGC circuit 3 to demodulate a reception signal S1 to provide an output of a voice signal S2. A noise detection section 11 of a squelch circuit 1 counts number of times of zero crossing of the voice signal S2 within a prescribed time and discriminates a noise included in the voice signal S2 to be within a permissible limit based on the count to provide an output of a noise detection signal Cn. An AGC voltage storage section 13 stores an AGC voltage Dn when the noise in the voice signal reaches the permissible limit based on the noise detection signal Cn. A squelch setting voltage calculation section 14 calculates a mean value between the AGC voltage Ds and the Dn to provide an output of a squelch setting voltage Do. A comparator section 15 compares the squelch setting voltage Do with the AGC voltage Ds. A switch 16 is used to switch on/off the voice signal $2 depending on the comparison result of the comparator section 15.

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 applicable to a mobile radio receiver or the like in which the reception state of a received signal changes.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing an example of a conventional squelch circuit. Here, the receiver 2 uses the AGC circuit 3
The received signal S1 is demodulated and the audio signal S2 is output while controlling the gain according to the AGC voltage Vs generated by. The squelch circuit 4 performs a squelch operation by blocking the passage of the audio signal S2 containing noise of an allowable amount or more.

If the AGC control is performed such that the gain of the receiver 2 increases as the AGC voltage Vs decreases, the gain of the receiver 2 increases as the input level of the received signal S1 decreases. The amount of noise included in the audio signal S2 increases. Now, assuming that when the AGC voltage Vs decreases and the gain of the receiver 2 increases and Vs = Vo, the noise amount included in the audio signal S2 reaches the allowable limit, this voltage Vo is set to the squelch setting voltage. Is preset by the voltage adjusting circuit 41. The comparison circuit 42 compares the AGC voltage Vs and the squelch setting voltage Vo, and Vs> Vo
In the case of, the switch 43 is turned on, and Vs ≦ V
When it is o, the switch 43 is controlled so that the switch 43 is turned off. Thus, the squelch operation is performed by detecting that the noise amount of the audio signal S2 has reached the allowable limit due to the level reduction of the reception signal S1 based on the AGC voltage Vs.

[0004]

In the above-described conventional squelch setting voltage, the AGC voltage at which the noise amount of the audio signal becomes the allowable limit due to the decrease of the received signal level is set in advance as the squelch setting voltage. And AG
By controlling ON / OFF of the switch by comparing with the C voltage, it is possible to prevent output of a voice signal containing a large amount of noise, which is more than the allowable amount. However, there may be a lot of noise even if the received signal level is high, or there may be little noise even if the received signal level is low.Therefore, in order to perform an appropriate squelch operation, the squelch setting should be made according to the reception state of the received signal. It is necessary to adjust the voltage to an optimum value, and therefore, when applied to mobile radio receivers, etc. where the reception state of the received signal changes, the complicated squelch setting voltage adjustment operation must be frequently performed. Have a point.

It is an object of the present invention to provide a squelch circuit which can automatically realize an appropriate squelch operation without frequently performing a complicated squelch setting voltage adjusting operation even when the reception state of a received signal changes. It is in.

[0006]

The squelch circuit of the present invention is a squelch circuit for performing a squelch operation on an output audio signal of a receiver for demodulating a received signal while controlling a gain according to an AGC voltage. Noise detection means for detecting that the amount of noise included in the signal is at the allowable limit,
When the noise detecting means detects that the amount of noise included in the output audio signal is within the allowable limit, the AG
AGC voltage storage means for storing the value of the C voltage, and this AG
Squelch setting voltage calculation means for calculating an average value of the AGC voltage value stored in the C voltage storage means and the value of the AGC voltage for controlling the gain of the receiver, and the AGC voltage for controlling the gain of the receiver. Comparing means for comparing the average value calculated by the squelch setting voltage calculating means, and a switch means for performing on / off operation according to the comparison result of the comparing means to control the transmission of the output audio signal. Prepare Further, the noise detection means, a zero-cross detection circuit for detecting the zero-cross point passage of the output audio signal,
A counter that periodically counts the number of times of zero-cross point detection detected by this zero-cross detection circuit within a predetermined time, and determines that the amount of noise included in the output audio signal is an allowable limit based on the count value of this counter. A configuration including a determination circuit may be used.

[0007]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Here, the receiver 2 controls the gain according to the AGC voltage Vs generated by the AGC circuit 3, demodulates the reception signal S1, and outputs the audio signal S2. The squelch circuit 1
The squelch operation is performed by blocking the passage of the audio signal S2 containing a noise of an allowable amount or more.

In the squelch circuit 1, the noise detecting section 11 for detecting that the noise amount contained in the audio signal S2 has reached the allowable limit, and the AGC voltage Vs are digitized to generate the AG signal.
The A / D conversion unit 12 that outputs the C voltage Ds and the AG when the noise amount included in the audio signal S2 reaches the allowable limit
The AGC voltage storage unit 13 for storing the C voltage value, the squelch setting voltage calculation unit 14 for calculating the squelch setting voltage Do, the comparison unit 15 for comparing the squelch setting voltage Do with the AGC voltage Ds, and the comparison result. And a switch 16 for turning on / off the audio signal S2.

As shown in FIG. 1, the noise detecting section 11 is
A zero-cross detection circuit 111 that detects when the audio signal S2 passes through a zero-cross point, a counter 112 that periodically counts the number of zero-crosses within a predetermined time, and a counter 1
The count value of 12 determines that the amount of noise included in the audio signal S2 has reached the allowable limit, and outputs the noise detection signal Cn.

Here, for example, the counting time of the counter 112 is 20 ms, and the voice band is 300 Hz to 3000 H.
If z is set and the noise included in the audio signal S2 is small, the count value of the counter is in the range of “6” to “60”. In addition, when the noise becomes large, the frequency of the noise is 5k.
Since it is above Hz, the count value of the counter is above "100". That is, the noise amount can be determined by the count value of the counter 112. It should be noted that, in determining the noise amount, it is possible to make a more reliable determination by validating only when the count value of a plurality of times continues to be the same value, for example, when the count value is the same count value three or more times out of five times. It can be performed.

The AGC voltage storage unit 13 includes a noise detection unit 11
When the noise detection signal Cn is received from, that is, the digitized AGC voltage Ds at the time when the amount of noise included in the audio signal S2 reaches the allowable limit is stored, and the stored A
The GC voltage is output as the limit AGC voltage Dn.

The squelch set voltage calculation unit 14 receives the AGC voltage Ds and the limit AGC voltage Dn, calculates the average value (Ds + Dn) / 2 of these two voltages, and outputs this as the squelch set voltage Do. The comparison unit 15 compares the squelch setting voltage Do and the AGC voltage Ds and outputs a control signal Cs for turning on / off the switch 16. The switch 16 controls passage of the audio signal S2 according to the control signal Cs.

For example, assume that the AGC control is performed such that the AGC voltage Vs decreases and the gain of the receiver 2 increases as the input level of the reception signal S1 decreases.
When the value of the limit AGC voltage Dn stored in the voltage storage unit 13 is “20” and the reception intensity is “100” as the value of the AGC voltage Ds, the squelch setting voltage Do = (D
Since s + Dn) / 2 = (100 + 20) / 2 = 60, the switch 16 is turned on when the input level of the reception signal S1 exceeds “60” as the value of the AGC voltage Ds, that is, when Ds> Do. The audio signal S2 is passed as. In addition, the input level of the reception signal S1 decreases, and A
If the value of the GC voltage Ds becomes "60" or less, that is,
When Ds ≦ Do, the switch 16 is turned off to prevent passage of the audio signal S2.

Further, the reception intensity becomes weak and the AGC voltage D
When the value of s decreases to “50”, the squelch setting voltage Do = (Ds + Dn) / 2 = (50 + 20) / 2
= 35, the input level of the received signal S1 is AGC.
If the value of the voltage Ds exceeds “35”, that is, D
When s> Do, the switch 16 is turned on and the audio signal S
2, but the input level of the received signal S1 is AGC
If the value of the voltage Ds becomes "35" or less, that is,
When Ds ≦ Do, the switch 16 is turned off to prevent passage of the audio signal S2.

By doing so, an appropriate squelch setting voltage can be automatically set according to the reception state of the received signal, and an appropriate squelch operation can be executed.

The noise detecting section 11 may be so constructed that a noise component is extracted by a filter and amplified and detected.

[0018]

As described above, according to the present invention, A
In a squelch circuit that performs a squelch operation on a voice signal output by a receiver that demodulates a received signal while controlling the gain according to the GC voltage, the AGC voltage value when the noise amount included in the voice signal is an allowable limit is calculated. The average value of the stored AGC voltage value and the stored AGC voltage value is calculated as a squelch set voltage, and the squelch set voltage and the AG are set.
By comparing with the C voltage and controlling the on / off of the audio signal according to the comparison result, an appropriate squelch setting voltage can be automatically set according to the reception state of the reception signal, and an appropriate squelch operation can be executed. .

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an example of a conventional squelch circuit.

[Explanation of symbols]

 11 Noise Detection Section 12 A-D Conversion Section 13 AGC Voltage Storage Section 14 Squelch Setting Voltage Calculation Section 15 Comparison Section 16 Switch 111 Zero Cross Detection Circuit 112 Counter 113 Judgment Circuit Cn Noise Detection Signal Dn Limit AGC Voltage Ds, Vs AGC Voltage S1 Reception Signal S2 Audio signal

Claims (2)

[Claims] 1. In a squelch circuit that performs a squelch operation on an output audio signal of a receiver that controls a gain according to an AGC voltage and demodulates a received signal, an amount of noise included in the output audio signal is an allowable limit. And a value for the AGC voltage that is stored when the noise detection unit detects that the amount of noise included in the output audio signal is at an allowable limit.
GC voltage storage means, the AGC voltage value stored in the AGC voltage storage means, and the A for controlling the gain of the receiver.
Comparing the squelch setting voltage calculating means for calculating an average value with the value of the GC voltage, and comparing the value of the AGC voltage for controlling the gain of the receiver with the average value calculated by the squelch setting voltage calculating means. A squelch circuit comprising: a means and a switch means for performing an on / off operation to control transmission of the output audio signal in accordance with a comparison result of the comparison means. 2. The noise detection means, a zero-cross detection circuit for detecting passage of a zero-cross point of the output audio signal,
A counter that periodically counts the number of times of zero-cross point detection detected by this zero-cross detection circuit within a predetermined time, and determines that the amount of noise included in the output audio signal is an allowable limit based on the count value of this counter. The squelch circuit according to claim 1, further comprising a determination circuit.