JP2000353967A - Noise squelch switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise squelch switching circuit for easily setting a squelch level regardless of the set value of a squelch volume. SOLUTION: This noise squelch switching circuit in an FM radio receiver controls the on/off of a squelch switch 3 on the basis of a noise level corresponding to the set value of a squelch volume 11. When the set value of the squelch volume 11 is equal to or greater than a preliminarily decided prescribed value, the gain of a noise amplifier 8 for amplifying a noise detected from an FM demodulated output is increased under the control of a control circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise squelch switching circuit in an FM radio receiver.

[0002]

2. Description of the Related Art A conventional noise squelch switching circuit 100 in an FM radio receiver supplies a demodulated output signal output from an FM demodulation circuit (FMIC) 1 to an audio amplifier 2 for amplification, as shown in FIG. The amplified output signal is supplied to an audio amplifier 4 via a squelch switch 3, amplified, and converted into a sound by a speaker 5.

The above-described noise squelch switching circuit 100
Further amplifies the FM demodulated output signal by an amplifier 6, passes the signal through a high-pass filter 7 having a cutoff frequency of about 20 kHz, detects a noise component, amplifies the noise component by a noise amplifier 8, and amplifies the noise component. The output from the rectifier circuit 9 is rectified by a rectifier circuit 9, and the rectified output is supplied to a control circuit 10a composed of, for example, a microcomputer, and the squelch volume (VOL) 11 supplied to the control circuit 10a for setting the squelch level is set. The control circuit 10a switches the squelch switch 3 on and off based on the value.

The above-described conventional noise squelch switching circuit 1
In the case of 00, the output level from the noise amplifier 8 changes according to the input signal level of the FM radio receiver. An example of this is shown in FIG. 9A in which the horizontal axis indicates the input signal level of the FM radio receiver, and the vertical axis indicates the noise level which is the output level of the noise amplifier, and the horizontal axis indicates the FM level. FIG. 9B shows the input signal level of the wireless receiver and the output voltage of the rectifier circuit 9 on the vertical axis.

Further, the squelch control shown by setting the squelch volume 11 on the horizontal axis and the output voltage of the rectifier circuit 9 on the vertical axis corresponds to the set value of the squelch volume 11, as shown in FIG. When the voltage is equal to or higher than the rectified output voltage, the squelch switch 3 is opened (off), the audio signal to the speaker 5 is cut off, and the squelch volume 11
When the voltage is less than the rectified output voltage corresponding to the set value, the squelch switch 3 is closed (turned on) and an audio signal is supplied to the speaker 5. Therefore, the receiver adjusts the set value of the squelch volume 11 while listening to the sound from the FM wireless receiver.

In the adjustment of the squelch volume 11, the squelch switch 3 is not closed unless the set value of the squelch volume 11 is higher and the rectified output voltage is lower, that is, the input signal level is not higher. As the value is smaller, the squelch switch 3 is closed even if the rectified output voltage is larger, that is, even if the input signal level is smaller.

[0007]

However, in the case of the above-mentioned conventional squelch switching circuit, FIG.
As shown in FIG. 9B and FIG. 10, when the input signal level of the FM radio receiver increases, the noise level decreases, but the change amount decreases. Conversely, as the input signal level of the FM radio receiver decreases, the noise level increases but the amount of change decreases. When the amount of change in the noise level decreases, there is a problem in that setting of the squelch level for turning on / off the squelch switch corresponding to the set value of the squelch volume 11 becomes difficult in the control circuit 10a.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a noise squelch switching circuit in which a squelch level can be easily set regardless of a set value of a squelch volume.

[0009]

SUMMARY OF THE INVENTION A noise squelch switching circuit according to the present invention is a circuit for switching a squelch switch on and off based on a noise level corresponding to a set value of a squelch volume.
The noise squelch switching circuit in the FM radio receiver that controls off is provided with control means for controlling the gain of amplification means for substantially amplifying the noise level based on the set value of the squelch volume.

According to the noise squelch switching circuit according to the present invention, since the noise level is substantially amplified by the amplifying means based on the set value of the squelch volume by the control means, the noise level is substantially increased. Therefore, the setting of the squelch level becomes easy regardless of the setting value of the squelch volume.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A noise squelch switching circuit according to the present invention will be described below with reference to an embodiment.

FIG. 1 is a block diagram showing a configuration of a noise squelch switching circuit according to an embodiment of the present invention.

A noise squelch switching circuit 20 according to an embodiment of the present invention supplies a demodulated output signal output from an FM demodulation circuit 1 to an audio amplifier 2 to amplify the signal, and amplifies the output signal via a squelch switch 3. The audio signal is supplied to an audio amplifier 4, amplified, and converted into a sound by a speaker 5.

The above-described noise squelch switching circuit 20 includes:
Further, the FM demodulated output signal is amplified by the amplifier 6 and
The noise component is detected by passing through a high-pass filter 7 having a cutoff frequency of about 20 kHz, the noise component is amplified by a noise amplifier 8, the output from the noise amplifier 8 is rectified by a rectifier circuit 9, and the rectified output is The squelch switch 3 is turned on and off by the control circuit 10 based on an output from a squelch volume (VOL) 11 supplied to the control circuit 10 for setting a squelch level. When the set value of the squelch volume 11 is 1 to α (α is a natural number) and when the set value of the squelch volume 11 is (α + 1) or more, the noise amplifier 8 is controlled by the control circuit 10.
Is switched.

Here, it is assumed that the set value of the squelch volume 11 is set stepwise.

When the output voltage is equal to or higher than the rectified output voltage corresponding to the set value of the squelch volume 11, the squelch switch 3 is opened (turned off), and the audio signal to the speaker 5 is cut off. When the output voltage is less than the rectified output voltage, the squelch switch 3 is closed (turned on), and an audio signal is supplied to the speaker 5.

The noise amplifier 8 has an operational amplifier OP to which a feedback resistor R3 is connected, for example, as shown in FIG.
R selectively connected by the resistor R1 and the switch S1
2, the output of the high-pass filter 7 is input to the operational amplifier OP through the series circuit, and when the set value of the squelch volume 11 is equal to or more than (α + 1) by the control circuit 10, the switch S1 is controlled to the on state to reduce noise. The gain of the amplifier 8 is increased from the normal set gain, and when the set value of the squelch volume 11 is 1 to α, the switch S1 is controlled to the off state to return the gain of the noise amplifier 8 to the normal set gain. Control.

Therefore, when the set value of the squelch volume 11 is 1 to α, the output of the high-pass filter 7 is amplified by the noise amplifier 8 having a normal set gain, and when the set value of the squelch volume 11 is equal to or more than (α + 1). , The gain of the noise amplifier 8 is increased from the normal set gain, and the output of the high-pass filter 7 is amplified by the noise amplifier 8 having the increased gain.
Is output as shown by the solid line in FIG. 2A, and is discontinuous when the set value of the squelch volume 11 is 1 to α and when the set value of the squelch volume 11 is equal to or more than (α + 1). Thus, when the set value of the squelch volume 11 is equal to or more than (α + 1), the output from the noise amplifier 8 increases as compared with the case of FIG. The output from the noise amplifier 8 is sent to the rectifier circuit 9.

Therefore, the output from the rectifier circuit 9 obtained by rectifying the output of the noise amplifier 8 is obtained when the set value of the squelch volume 11 is 1 to α, as shown by the solid line in FIG. When the value is greater than or equal to (α + 1), the output becomes discontinuous. When the set value of the squelch volume 11 is greater than or equal to (α + 1), the rectified output increases as compared with the case of FIG. 9B. The output from the rectifier circuit 9 is sent to the control circuit 10.

Here, when the output voltage is equal to or higher than the rectified output voltage corresponding to the set value of the squelch volume 11, the squelch switch 3 is opened (turned off) and the audio signal to the speaker 5 is cut off. When the voltage is less than the corresponding rectified output voltage, the squelch switch 3 is closed (turned on) and an audio signal is supplied to the speaker 5. However, as described above, the output voltage from the rectifier circuit 9 with respect to the output from the rectifier circuit 9 and the set value of the squelch volume 11 is as shown by the solid line in FIG. 3, and the set value of the squelch volume 11 is (α + 1) or more. At this time, the rectified output voltage increases as compared with the case of FIG. 10, and the amount of change in the rectified output voltage increases. Therefore, the squelch level can be easily set regardless of the squelch volume setting value.

The above-described noise squelch switching circuit 2
0, a resistor R0 selectively connected to the noise amplifier 8 by a switch S2 as shown in FIG.
Are further connected to form a resistor R0, a resistor R1, and a switch S1.
When the set value of the squelch volume 11 is equal to or more than (α + 1) by the control circuit 10, the output of the high-pass filter 7 is input to the operational amplifier OP through a series circuit with R2 selectively connected by The switch S1 and the switch S2 are turned on to increase the gain of the noise amplifier 8 from the normal set gain. When the set value of the squelch volume 11 is (β + 1) to α, the switch S2 is turned on, and The switch S1 is turned off to return the gain of the noise amplifier 8 to the normal set gain, and the set value of the squelch volume 11 is 1 to β
In this case, the switch S2 is controlled to be off and the switch S1 is controlled to be off, so that the gain of the noise amplifier 8 is reduced below the normal set gain. Here, β is a natural number, and α is a value larger than (β + 1).

As described above, by configuring the gain of the noise amplifier 8 to be switched in three stages according to the set value of the squelch volume 11, when the set value of the squelch volume 11 is (β + 1) to α and (α +
1) In the case described above, the gain of the noise amplifier 8 is set to 2
When the set value of the squelch volume 11 is 1 to β, it is the same as the case of switching to the stage.
(B) and the portion indicated by the broken line in FIG. 3 are added, and the set value of the squelch volume 11 is 1 to β
In other words, even when the change amount of the rectified voltage is small, the setting of the squelch level becomes easy, and the setting of the squelch level becomes easy regardless of the set value of the squelch volume 11.

Next, a description will be given of a first modification of the noise squelch switching circuit according to one embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a first modified example of the noise squelch switching circuit according to one embodiment of the present invention.

The noise squelch switching circuit 30 according to the first modification includes a high-pass filter 71 in place of the high-pass filter 7 in the noise squelch switching circuit 20, and a cut-off frequency of the high-pass filter 71 in place of gain switching of the noise amplifier. Is switched based on the set value of the squelch volume 11.

In the noise squelch switching circuit 30, when the set value of the squelch volume 11 is equal to or more than (α + 1), the cutoff frequency of the high-pass filter 71 is set to 10
By setting the frequency to kHz, the noise component of 10 kHz to 20 kHz output from the high-pass filter 71 increases, so that the noise level can be substantially increased, which is equivalent to increasing the gain of the noise amplifier 8. Becomes When the set value of the squelch volume 11 is 1 to α, the cutoff frequency of the high-pass filter 71 is set to 20 kHz, so that the noise amplifier 8
Is equivalent to a case where the gain is set to a normal gain.

As a result, the noise squelch switching circuit 30
As with the noise squelch switching circuit 20 according to the embodiment of the present invention, the setting of the squelch level becomes easy regardless of the set value of the squelch volume.

Next, a description will be given of a second modification of the noise squelch switching circuit according to one embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a second modified example of the noise squelch switching circuit according to one embodiment of the present invention.

The noise squelch switching circuit 40 according to the second modified example includes an attenuation circuit 1
2, a demodulation output signal from the FM demodulation circuit 1 is supplied to the amplifier 6 via the attenuation circuit 12, and the control circuit 10 replaces the gain switching of the noise amplifier 8 with the set value of the squelch volume 11. Attenuation circuit 12 based on
This is an example in which the attenuation rate is switched.

In the noise squelch switching circuit 40, when the set value of the squelch volume 11 is equal to or more than (α + 1), the attenuation rate of the attenuation circuit 12 is reduced from the set attenuation rate under the control of the control circuit 10. As a result, the noise level can be substantially increased, and the noise amplifier 8
Is equivalent to increasing the gain of. Further, when the set value of the squelch volume 11 is a set value of 1 to α, by returning the attenuation rate of the attenuation circuit 12 to the set attenuation rate, it becomes equivalent to the gain of the noise amplifier 8 being set to a normal gain.

As a result, the noise squelch switching circuit 40
As with the noise squelch switching circuit 20 according to the embodiment of the present invention, the setting of the squelch level becomes easy regardless of the set value of the squelch volume.

Next, a description will be given of a third modified example of the noise squelch switching circuit according to one embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a third modification of the noise squelch switching circuit according to one embodiment of the present invention.

In the noise squelch switching circuit 50 according to the third modification, the noise squelch switching circuit 20 is further provided with a switch 13, an amplifier 6a, a high-pass filter 7a, a noise amplifier 8a, and a rectification circuit 9a. A voltage is also supplied to the control circuit 10, and a demodulated output signal from the FM demodulation circuit 1 is supplied to the amplifier 6 or 6a via the switch 13. The control circuit 10 replaces the gain switching of the noise amplifier 8. This is an example in which the switch 13 is switched based on the set value of the squelch volume 11. The gain of the noise amplifier 8a is set to be larger than the gain of the noise amplifier 8.

In the noise squelch switching circuit 50, when the set value of the squelch volume 11 is equal to or more than (α + 1), the demodulated output signal output from the FM demodulation circuit 1 by the switch 13 under the control of the control circuit 10. Is supplied to the amplifier 6a, the noise level can be substantially increased, which is equivalent to increasing the gain of the noise amplifier 8. When the set value of the squelch volume 11 is a set value of 1 to α, the switch 13 supplies a demodulated output signal output from the FM demodulation circuit 1 to the amplifier 6 under the control of the control circuit 10, The noise level can be substantially restored to the original level, which is equivalent to the case where the gain of the noise amplifier 8 is set to a normal gain.

As a result, the noise squelch switching circuit 50
As with the noise squelch switching circuit 20 according to the embodiment of the present invention, the setting of the squelch level becomes easy regardless of the set value of the squelch volume.

[0038]

As described above, according to the noise squelch switching circuit of the present invention, the amount of change in the noise level is increased in the portion where the amount of change in the noise level is small.
The effect is obtained that the setting of the squelch level for turning on / off the squelch switch corresponding to the set value of the squelch volume 11 is facilitated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a noise squelch switching circuit according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining an operation of the noise squelch switching circuit according to the embodiment of the present invention;

FIG. 3 is an explanatory diagram for explaining an operation of the noise squelch switching circuit according to the embodiment of the present invention;

FIG. 4 is a block diagram showing a configuration of a noise amplifier in the noise squelch switching circuit according to one embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a first modified example of the noise squelch switching circuit according to one embodiment of the present invention;

FIG. 6 is a block diagram showing a configuration of a second modified example of the noise squelch switching circuit according to one embodiment of the present invention;

FIG. 7 is a block diagram showing a configuration of a third modified example of the noise squelch switching circuit according to one embodiment of the present invention;

FIG. 8 is a block diagram showing a configuration of a conventional noise squelch switching circuit.

FIG. 9 is an explanatory diagram for explaining an operation of a conventional noise squelch switching circuit.

FIG. 10 is an explanatory diagram for explaining an operation of a conventional noise squelch switching circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 FM demodulation circuit 2 and 4 Audio amplifier 3 Squelch switch 5 Speaker 6 and 6a Amplifier 7, 7a and 71 High pass filter 8 and 8a Noise amplifier 9 and 9a Rectifier circuit 10 and 10a Control circuit 11 Squelch volume 12 Attenuator 13 Switch 20, 30, 40 and 50 noise squelch switching circuit

Claims (3)

[Claims] 1. A noise squelch switching circuit in an FM radio receiver for controlling ON / OFF of a squelch switch based on a noise level corresponding to a set value of a squelch volume, wherein the noise level is substantially set based on the set value of the squelch volume. A noise squelch switching circuit, further comprising control means for controlling the gain of amplifying means for amplifying the noise. 2. The noise squelch switching circuit according to claim 1, wherein the control means controls the gain of the amplifying means in a range of the set value of the squelch volume where a change amount of the noise level is small with respect to a change of the set value of the squelch volume. A noise squelch switching circuit characterized by substantially increasing. 3. The noise squelch switching circuit according to claim 1, wherein said amplification means is means for substantially amplifying the level of noise detected from the FM demodulated output.