JPH0354921A - Squelch signal generating circuit - Google Patents

Abstract

PURPOSE:To prevent the generation of misjudgement by holding voltage corresponding to the minimum value of intermediate frequency outputs. CONSTITUTION:An intermediate frequency output outputted from a radio wave receiver 1 is supplied to a level measuring circuit 4 in a squelch signal generating circuit 20 through a band pass filter 2 and converted into voltage corresponding to the level of the intermediate frequency output. The minimum value of outputs x4 from the circuit 4 is held by a holding circuit 5 and compared with a reference value by a comparator 6 to obtain a squelch signal x6. On the other hand, the output x2 of the band pass filter 2 demodulated by a demodulator 7 through an amplifier 3 to obtain a base band waveform. The output of the demodulator 7 is supplied to an electronic switch 8. When the squelch signal x6 is sent, the switch 8 is turned on to send the base band waveform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a squelch signal generation circuit for a wireless device that has a function of determining whether or not there is a radio wave generated from a wireless device of another station. In particular, based on this judgment result, you can decide whether or not to start up your own wireless device and emit radio waves.
Alternatively, the present invention can be effectively utilized when deciding whether or not to output a received audio signal from a speaker or the like.

[Conventional technology]

A conventional squelch signal generation circuit inputs the intermediate frequency output of a radio receiving device to a level measuring circuit that outputs a voltage according to its level, and calculates the average value of the output of the level measuring circuit using a low-pass filter, etc. A method was used in which the average value was determined in advance and compared to see whether it was above or below the voltage corresponding to a predetermined level.

[Problem to be solved by the invention]

Conventional squelch signal generation circuits had the disadvantage of being susceptible to external noise because they judged whether or not there was a radio wave from another station based on the "temporal average value" of the output of the level measurement circuit. .

In other words, when external noise is added, the level measurement circuit also calculates the average value of the external noise, making it impossible to distinguish whether or not there is a difference due to radio waves emitted from other stations. There was a phenomenon in which the receiver assumed that there was a radio wave from another station even when the radio signal was being received, and made a wrong decision. As a result, there were problems such as not being able to start up the wireless device of the local station forever, or even noise being output as sound from the speaker.

An object of the present invention is to provide a squelch signal generation circuit free from such drawbacks.

[Means to solve the problem]

The squelch signal generation circuit of the present invention includes: a level measuring circuit that converts an intermediate frequency output of a radio receiving device into a voltage according to a level; and a voltage corresponding to the smallest value of the intermediate frequency output for the output of the level measuring circuit. The present invention is characterized by comprising a hold circuit that holds the voltage, and a comparator that generates a squelch signal by comparing the output of the hold circuit with a predetermined voltage.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The squelch signal generating circuit 20 of this embodiment includes a level measuring circuit 4 that converts the intermediate frequency output of a radio receiving device into a voltage corresponding to its level, and the output of this level measuring circuit.
It has a hold circuit 5 that holds a voltage corresponding to the smallest value of the intermediate frequency output, and a comparator 6 that compares the output of this hold circuit with a predetermined voltage and generates a squelch signal.

As an example, the hold circuit 5 is shown as having a time constant circuit consisting of a resistor 12 and a capacitor 13, and a diode 11 connected in parallel to the resistor 12 of the time constant circuit. The orientation of the diode 11 is selected so that if the voltage across the capacitor l3 is higher than the human input voltage to the hold circuit 5, current will flow through the diode. By doing this, a low input voltage is held in the capacitor 13.

In FIG. 1, 1 is a radio receiving device, 2 is a bandpass filter, 3 is an amplifier, 7 is a demodulator, 8 is an electronic switch, 9 is a power amplifier, and 10 is a speaker.

Next, the operation of this embodiment will be explained with reference to the signal waveform diagram of each part in FIG.

The intermediate frequency output output from the radio receiving device (RX) 1 passes through a bandpass filter 2 that limits the band, and the output X2 of the bandpass filter 2 is measured by the level measurement circuit 4 of the squelch signal generation circuit 20 to determine the level of the intermediate frequency output. It is converted to a voltage according to the voltage.

The output x4 of the level measuring circuit 4 is held at the minimum value by the hold circuit 5, and the output x4 of the hold circuit
A squelch signal X is obtained by further comparing the signals in a comparator 6.

On the other hand, the output χ2 of the bandpass filter 2 passes through the amplifier 3 and is demodulated by the demodulator 7 to obtain a baseband waveform. This output passes through an electronic switch (SW) 8, is power amplified by a power amplifier 9, and is output as sound from a speaker 10. Here, the electronic switch 8 is turned on when the squelch signal x6 is rising indicating that the signal is being received. Now, in Fig. 2, Fig. 2 (A) shows that the carrier is actually present and the signal is being received. FIG. 2(B) shows the signal waveforms of each part when only noise is present and no signal is being received. 2(A) and 2(B), (1) shows the waveform of the output x2 of the bandpass filter 2, (II) shows the waveform of the output x4 of the level measuring circuit 4, the output x of the hold circuit 5, The waveform of (
1) shows the waveform of the output xb (squelch signal) of the comparator 6.

If carrier CA actually exists and noise N, is added during signal reception, as shown in N) of FIG. N,
The voltage level changes accordingly. The hold circuit 5 holds the minimum value of this voltage level and sends the output X to the comparator 6.

The reference voltage of comparator 6 is set to V. Then, when the signal X exceeds v0, the squelch signal χ6 rises. During signal reception, the carrier C, is stable and at a sufficient level, so the squelch signal X, rises during this period as shown by (I[[). Therefore, even if the noise N is added, in this case the carrier CA is actually present at the same time, so it can be said that the correct operation is when the squelch signal X6 rises.

On the other hand, when only the noise N2 is input as shown in (1) of FIG. 2(B), the lowest value of the signal x4 output from the level measuring circuit 4 is held as shown in (n). Therefore, the signal X is the reference voltage ■. The probability of exceeding is significantly reduced.

Therefore, the squelch response due to external noise is significantly reduced, and the problem of hearing only noise from the speaker 10 is improved.

Among external noises, especially intermittent noises or generally common impulsive urban noises, the output X of the level measuring circuit 4 drops to a low value.
The signal X is also held at a low value, and the squelch signal generation circuit of the present invention functions effectively against this type of noise.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to more accurately determine whether radio waves have been emitted from the other station's wireless device without being affected by external noise, compared to conventional squelch signal generation circuits. Therefore, problems such as noise generated from the speaker due to external noise are significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the squelch signal generation circuit of the present invention, and FIG. 2 is a signal waveform diagram of each part of the squelch signal generation circuit of FIG. 1. ■... Radio receiving device 2...Band pass filter 3...Amplifier 4...Level measuring circuit 5...Hold circuit 6...Comparator 7... Demodulator 8... Electronic switch 9 - Power amplifier 10 - Speaker 20 - Squelch signal generation circuit

Claims (1)

[Claims] (1) A level measuring circuit that converts the intermediate frequency output of the radio receiving device into a voltage according to the level; and a hold circuit that holds the output of the level measuring circuit at a voltage corresponding to the smallest value of the intermediate frequency output. and a comparator that generates a squelch signal by comparing the output of the hold circuit with a predetermined voltage.