JPS62216427A - Squelch circuit - Google Patents

Abstract

PURPOSE:To prevent the malfunction of a tone squelch circuit due to noise by providing a gate circuit between a demodulator and the tone squelch circuit and controlling the gate circuit with the logic output of a noise squelch circuit and controlling a sound amplifier with the logic output of the tone squelch circuit. CONSTITUTION:When a receiver is in the waiting state, a noise component on the outside of the sound band outputted from a demodulator 1 is amplified selectively by a noise amplifier 3 and is detected by a noise detector 4, and the signal of logic value '0' is outputted to the gate terminal 14a of a gate circuit 14 from a noise squelch circuit 2 by an inverter circuit or the like included in the noise detector 4. Since the signal of logic value '0' is inputted to the gate terminal 14a, the gate circuit 14 is turned off. Consequently, a tone squelch circuit 7 is made unoperated because no signals are inputted to the input terminal of the circuit 7 at all, and the logic output of the output terminal is always '0'. Since noise is not inputted, the malfunction of the tone squelch is prevented as well.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a squelch circuit for a receiver that includes a tone squelch circuit that operates using a tone signal superimposed on an audio signal and a noise squelch circuit that operates using a noise signal component. It is related to.

[Conventional technology]

FIG. 2 is a block diagram showing a conventional squelch circuit.

In the figure, 1 is a receiving demodulator that outputs audio components, and 2 is composed of a noise amplifier 3 and a noise detection circuit 4, which outputs a signal with a logical value of "1" when the receiving input electric field is above a certain level. 5 is a low-pass filter that removes audio frequencies and outputs only tone frequencies; 6 is a low-pass filter that outputs excessive noise components and prevents the tone squelch circuit described below from malfunctioning due to tone frequency components in the noise. limiter circuit 7 for bandpass filter 8. A tone squelch circuit is composed of a tone amplifier 9 and a tone detection circuit 10, and outputs a signal with a logical value of "1" when detecting a tone signal with a frequency unique to the circuit; 11 is an AND circuit; 12 is an input terminal 12
a, an audio amplifier comprising a control terminal 12b and an output terminal 12c, which is turned on when an on control signal is input to the control terminal 12b, and outputs an audio signal from an output terminal 12C; 13, a speaker; Note that the tone frequency used in the tone squelch circuit 7 is about 67 Hz to
sb at 250Hz, the lower part of the audio band 300H2-3KHz is used.

Next, the operation of the squelch circuit having the above configuration will be explained. First, when the receiver is in standby mode, noise components outside the audio band output from the demodulator 1 are selectively amplified by the noise amplifier 3 and then detected by the noise detector 4. A signal with a logical value of "0" is output from the noise squelch circuit 2 to the AND circuit 11 using an inverter circuit included in the noise squelch circuit 2. Therefore, since the AND circuit 11 receives a signal with a logical value of "0" at one input terminal, no output signal is output even if the logical value output from the tone squelch circuit 7 is 0. Therefore, the audio amplifier 12 is in an inoperable state because no on control signal is input to its control terminal 12b. Therefore, no sound is output from the speaker 13. Next, when the received input electric field modulated by the audio signal and tone signal is applied to the receiver 1, the noise component of the demodulated output from the demodulator 1 decreases, so the output of the noise detection circuit 4 becomes a logic The value becomes "1". Therefore, the noise squelch circuit 2 outputs an output signal of logical value rlJ to the AND circuit 11. Further, the tone signal component included in the demodulated output output from the demodulator 1 is input to the tone squelch circuit 7 via the low-pass filter 5 and the limiter circuit 6. Therefore, this tone signal component is transmitted to this tone squelch circuit 7.
When the tone signal component matches the unique frequency of the bandpass filter 8, the tone signal component passes through the bandpass filter 8, is amplified by the tone amplifier 9, and is detected by the tone detection circuit 10. Therefore, the tone squelch circuit 7 outputs an output signal of logical value "1" to the AND circuit 11. Therefore, since signals with a logical value of "1" are input to both of the two input terminals of this AND circuit 11, an ON control signal is output. Therefore, since the on control signal is input to the control terminal 12b of the audio amplifier 12, the audio amplifier 12 remains in the on state and outputs an audio signal to the speaker 13 from its output terminal 12C. Therefore, audio can be output from the speaker 13. In this way, only when the noise squelch circuit 2 determines that the received input electric field 1 is above a certain level and the tone squelch circuit 7 detects a tone signal with a frequency unique to that circuit, an on command is given to the audio amplifier 12. sound can be output from the speaker 13.

[Problems that the invention attempts to solve]

In the above-mentioned conventional squelch circuit, when the receiver is in standby mode, the noise component increases in the output of the demodulator 1, so the tone squelch circuit 7 detects the tone frequency component in the noise, and there is no tone signal. However, it may be determined that there is a tone, and the output logic value becomes "1", resulting in a malfunction. At this time, if the same line frequency modulated by another tone signal is received, the output logic value of the noise squelch circuit 2 becomes "1", so the audio amplifier 12 operates and the speaker 13 outputs audio. This may defeat the purpose of tone squelch circuit 7. In order to prevent malfunction of the tone squelch circuit I due to this noise, a limiter circuit 6 is connected to the input of the tone squelch Q child circuit 70.
was provided to prevent excessive noise from being input to the tone squelch circuit 7. However, by providing the limiter circuit 6, if there is a reception input that is excessively modulated with audio, the excessive audio output will be demodulated compared to the demodulator 1.
The tone signal superimposed on the audio signal is deleted by the limiter circuit 6, and the tone signal is not detected and becomes the output logic value rOJ of the tone squelch circuit 7, so the audio amplifier 12 does not operate and the audio output from the speaker 13 is interrupted. There were often cases.

Therefore, a low-pass filter 5 is provided to prevent the sound from being input to the tone squelch circuit 7, but in order to prevent the tone squelch circuit 7 from malfunctioning, it is necessary to significantly increase the number of stages of the low-pass filter 5. As a result, the limiter circuit 6 is required to prevent the tone squelch circuit 7 from malfunctioning due to noise, and the number of stages of the low-pass filter 5 increases to prevent malfunctions of the audio.

[Means for solving problems]

The squelch circuit of the present invention is constructed by providing a gate circuit between a demodulator and a tone squelch circuit, controlling the gate circuit with the logic output of the noise squelch circuit, and controlling an audio amplifier with the logic output of the tone squelch circuit. It is.

[Effect]

The present invention can prevent malfunctions of the tone squelch circuit due to noise, and therefore malfunctions due to voice can be prevented.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a squelch circuit according to the present invention. In the same figure, 14 is the gate terminal 1
When a signal with the output logical value "1" of the noise squelch circuit 2 is input to 4H, the gate circuit turns on, and passes the output signal of the low-pass filter 5 input to the input terminal 14b and outputs it from the output terminal 14C. be.

Next, the operation of the squelch circuit having the above configuration will be explained. First, when the receiver is in standby mode, noise components outside the audio band output from the demodulator 1 are selectively amplified by the noise amplifier 3, and then detected by the noise detector 4. A signal with a logical value of "0" is outputted from the noise squelch circuit 2 to the gate terminal 148K of the gate circuit 14 using an inverter circuit included in the noise squelch circuit 2. Therefore, this gate circuit 14 has its gate terminal 14
It is in an off state because a signal with a logical value of "0" is input to a.

Therefore, the tone squelch circuit 7 is not in an inoperative state because no signal is input to its input terminal, and the logic output of its output terminal is always a logic value "0". Furthermore, since no noise is input, malfunctions of the tone squelch circuit 7 are also eliminated. Therefore, the audio amplifier 12 is not inputted with the K-on control signal to its control terminal 12b and becomes inoperative. Therefore, no sound is output from the speaker 13. Next, when the receiving input electric field modulated by the audio signal and tone signal is applied to the receiver, the noise component of the demodulated output from the demodulator 1 decreases, so the output of the noise detection circuit 4 becomes a logic The value becomes "1". therefore,
The noise squelch circuit 2 outputs an output signal with a logical value of "1" to the gate terminal 14a of the gate circuit 14. For this reason,
This gate circuit 14 has a logic value "
1" signal is input and it becomes on state. Therefore, the tone signal component included in the demodulated output output from the demodulator 1 is input to the tone squelch circuit 7 via the low-pass filter 5 and the gate circuit 14 in an on state. Therefore, when this tone signal component matches the passing frequency of the bandpass filter 8 of this tone squelch circuit 7,
This tone signal passes through this bandpass filter 8, is amplified by a tone amplifier 9, and is detected by a tone detection circuit 10.

Therefore, the tone squelch circuit 7 outputs an output signal with a logical value of "1". Therefore, the audio amplifier 12 is not in the ON state because the ON control signal 8 is input to its control terminal 12b, and the audio signal is output from the output terminal 12c to the speaker 1.
3 is output. Therefore, audio can be output from the speaker 13.

In the above-described embodiment, the gate circuit 14 is provided to control the operation of the tone squelch circuit element using the output logic of the noise squelch circuit 2. However, the gate circuit 14 is not limited to this.
Of course, the output logic of the tone squelch circuit 7 may be controlled by controlling the power supply circuit (not shown) of the tone squelch circuit 7 using the output logic of the noise squelch circuit 2 without using the noise squelch circuit 2.

〔Effect of the invention〕

As described above in detail, according to the squelch circuit according to the present invention, it is possible to prevent malfunctions of the tone squelch circuit due to noise, and furthermore, malfunctions due to voice can be prevented.

Furthermore, since the number of stages of the low-pass filter can be reduced, the circuit configuration can be simplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a squelch circuit according to the present invention, and FIG. 2 is a block diagram showing a conventional squelch circuit. 1...Demodulator, 2...Noise squelch circuit, 3
...Noise amplifier, 4...Noise detection circuit, 5
・・Fist・Low pass filter, 6・・Pot limiter circuit,
7... Tone scourch circuit, 8... φ band pass filter, 9... φ tone amplifier, 10... Fist tone detection circuit, 11... Middle AND circuit 12111 Co.
Audio amplifier, 13... speaker, 14... gate circuit.

Claims (1)

[Claims] a noise squelch circuit to which the output signal of the demodulator is input; a gate circuit that is opened by the input of the output signal of the noise squelch circuit and allows the output signal of the demodulator to pass; and a tone squelch circuit to which the output signal of the gate circuit is input; A squelch circuit comprising: an audio amplifier that is controlled by input of an output signal of the tone squelch circuit and amplifies the output of the demodulator.