JPH0354922A - Squelch signal generating circuit - Google Patents

Abstract

PURPOSE:To prevent the generation of misjudgment by generating a pulse based upon an intermediate frequency output. CONSTITUTION:An intermediate frequency output outputted from a ratio wave receiver 1 is comverted into voltage corresponding to the level of the intermediate frequency output by a level measuring circuit 4 through a band pass filter(BPF) 2. An output x4 from the circuit 4 is sent to a pulse generating circuit 6 through a comparator 5 and a squeltch signal x6 to fall when the output x5 of the comparator 5 rises and to rise when the fall of the output x5 of the comparator 5 is continued for a response time is generated from the circuit 6. The output x2 of the BPF 2 is demodulated through an amplifier 3 and a demodulator 7 to obtain a base band waveform. Since an electroic switch 8 is ON during the rise of the squelch signal x6, the base band waveform is outputted during the ON of the switch 8.

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] In the conventional method, it was determined 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, making it vulnerable to external noise. There was a drawback.

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 precept due to radio waves emitted from other stations, and the level measuring circuit calculates the average value of the external noise as well. 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 have been 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 the intermediate frequency output of a radio receiving device into a voltage corresponding to its level, and a level measuring circuit that compares the output of the level measuring circuit with a voltage corresponding to a predetermined level. ,
a comparator circuit that outputs a signal that becomes a falling state when the output of the level measuring circuit is higher than the predetermined level, and a signal that becomes a rising state when the output of the level measuring circuit is smaller than the predetermined level; When the output of the comparator circuit falls and the output of the comparator circuit falls, the pulse generation circuit generates a signal that rises if this falling state continues for a predetermined period of time.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail 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.
a comparison circuit 5 for comparing with a voltage corresponding to a predetermined level;
A pulse generation circuit 6 that outputs a pulse that, once the output of this comparison circuit rises, remains falling for a certain response time even after the output of the comparison circuit falls.
It has

The pulse generation circuit 6 can be easily realized by a monostable multivibrator or the like, but the response time from when the output of the comparator circuit 5 falls to when the output of the pulse generation circuit 6 rises is, for example, After actually receiving the signal from the other station 7, so as not to affect the call 5
It is selected to be approximately 0lIlsec.

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 measurement circuit 4 is compared in the comparison circuit 5,
The output X of this comparison circuit is sent to the pulse generation circuit 6. The pulse generating circuit 6 generates a signal that falls when the output X of the comparator circuit 5 rises and rises when the output Xs falls and this falling state continues for the response time.

On the other hand, the output x2 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 amplified in power by a power amplifier 9, and is output as sound from the speaker 10. Here, the electronic switch 8 is turned on by the squelch signal X. This is when the device is standing up because it is receiving a signal.

Now, in Fig. 2, Fig. 2 (A) shows each signal XLXa, X5,
As shown in the waveform X2 of FIG. 2(A), the waveform of the carrier If C4 actually exists and noise N1 is added during signal reception, the voltage level of the output X4 of the level measuring circuit 4 changes in response to the noise N. In the comparator circuit 5, the output X4 is the reference voltage V. In comparison, the output X is in a falling state when the output X4 is greater than the reference voltage V4, and is in the rising state when the output
occurs. The rise of the output X, means that the carrier C, has disappeared. The pulse generation circuit 6 is
In response to output X, a squelch signal x. occurs.

During signal reception, carrier C, is stable and at a sufficient level, so squelch signal X. has been standing up for a while now. Therefore, even if noise N1 is added, carrier CA is actually present at the same time in this case, so it can be said that the correct operation is when the squelch signal X is in a rising state.

On the other hand, when only the noise N2 is input as shown in the waveform X2 of FIG.
4 is the reference voltage■. It is often lower than that. In particular, impulse urban noise is common among external noises, and this tendency can be seen. In this case, the waveform X falls only in the section where the noise level is high. However, unless this falling state continues for the response time T0, the squelch signal x6 will not rise. That is, waveform X
, falls, the squelch signal X6 does not suddenly rise, and the squelch signal x6 does not actually rise until response time T. Later.

In this way, even if the waveform x4 becomes higher than the reference voltage V0 due to noise or the like, it is not determined that a carrier has arrived during the response time T0.

As in the example shown in FIG. 2(B), there is noise N2 in the interval T2.
Assuming that is input, the average of the output x4 is the reference voltage ■. Even in cases where conventional squelch signal generation circuits generate noise from the squelch signal X, the squelch signal X, falls, and the phenomenon in which noise is output from the speaker 10 is significantly reduced. will be reduced to

〔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 generating circuit of the present invention, and FIG. 2 is a diagram of signal waveforms at various parts. 1... Radio receiving device 2... Bandpass filter 3... Amplifier 4... Level measurement circuit 5... Comparison circuit 6... Pulse generation Circuit 7...Demodulator 8...Electronic switch 9...Power amplifier 10...Subika 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 its level, and the output of the level measuring circuit is compared with a voltage corresponding to a predetermined level. a comparator circuit that outputs a signal that is in a falling state when the level measurement circuit output is greater than the predetermined level, and a signal that is in a rising state when the output of the level measurement circuit is smaller than the predetermined level; 1. A squelch signal generating circuit comprising: a pulse generating circuit that generates a signal that rises when the output of the circuit falls and this falling state continues for a predetermined period of time.