JPS6048624A - Squelch control circuit - Google Patents

Abstract

PURPOSE:To prevent a noise attended with the switching of a squelch circuit from being generated by opening forcibly the squelch when the fluctuation of an electric field is frequent. CONSTITUTION:Every time a reception electric field strength exceeding a prescribed value is detected, a pulse of a prescribed width is generated and when the pulse is integrated and a prescribed threshold value is exceeded, the signal is added to an electric field detecting signal so as to turn on/off the squelch circuit. A continuous reception sound signal is generated from an OR circuit 2 when the fluctuation of the electric field strength is frequent, an output signal of the OR circuit 2 is used as a squelch control signal in the squelch circuit, and when the signal is at a high level, the squelch circuit is turned off and when the signal is at a low level, the squelch circuit is turned on. Thus, when the reception electric field strength is sufficiently high, the continuous reception sound output is produced and also even if the fluctuation of the reception electric field strength is frequent, the continuous reception sound output is generated so as to prevent generation of noise attended with the frequent switching of the squelch circuit.

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to improvement of a squelch circuit in a radio telephone device, and in particular to reducing the influence of noise caused by opening and closing of the squelch circuit even when the received electric field strength fluctuates rapidly. This relates to a squelch control circuit that can perform

Prior Art and Problems In radio telephone devices, when the receiving electric field is weak, noise tends to be mixed into the received voice, causing discomfort to the listener. For this reason, a squelch circuit is generally used that eliminates noise by cutting off the received audio when the electric field strength decreases.

Squelch circuits normally operate well and are extremely effective when the received field strength is constant. However, when the received electric field strength fluctuates sharply, the squelch opens and closes frequently, and the generation of transient noise caused by the opening and closing of the squelch circuit causes a problem in that the sound becomes difficult to hear.

Conventionally, one way to reduce the noise caused by the frequent opening and closing of squelch circuits was to reduce the frequency of squelch circuit operation by adding hysteresis to its operation, but if the fluctuations in the electric field are too large, is not very effective. Also, reducing the squelch operation frequency by delaying the squelch operation will improve the situation to some extent, but if there is a pulsed electric field input (noise), the noise output will increase due to the squelch circuit's operation delay, making it extremely noisy. .

Purpose of the Invention The present invention is intended to solve the problems of the prior art, and its purpose is to forcibly open the squelch when the electric field intensity fluctuates rapidly, thereby stabilizing the electric field intensity. An object of the present invention is to provide a squelch control circuit that can reduce the influence of noise accompanying the opening and closing of the squelch circuit even when the electric field strength fluctuates rapidly by opening and closing the squelch according to changes in the electric field strength. .

Embodiment of the Invention FIG. 1 shows an embodiment of the squelch control circuit of the invention. In the same figure, 1 is a monostable multipipe lake (hereinafter abbreviated as monomultiply), 2 is an OR circuit,
D is a diode, C is a capacitor, and R is a resistor.

Also, Figure 2 shows the numbers of each part in the circuit of Figure 1, and
is an electric field detection signal obtained by a receiving circuit (not shown) corresponding to the input electric field strength, and is a high level (
H), and when the electric field strength is lower than this, the low level (
L), for example, the detected output of the received signal corresponds to this.

■ is the output signal of the monomulti 1, ■ is the output of the integrating circuit consisting of a capacitor C2 and a resistor R, and ■ is the output signal of the OR circuit 2. These signals are given the same numbers and correspond to each other in Figure 1. It is also shown in the position.

As shown in Figure 2, the electric field detection signal ■ changes from high level to low level depending on whether the electric field strength exceeds the electric field detection threshold 7 hold level SE from the start of reception to the end of reception. , when the electric field strength fluctuates rapidly, the frequency of changes increases.

The monomulti 1 is triggered by the rising edge of the electric field detection signal (2) and generates an output signal (@) consisting of pulses of a constant width. The output signal @ is rectified through a diode D and smoothed by an integrating circuit consisting of a capacitor C1 and a resistor R to produce an output ■. The electric field detection signal ■ and the output ■ of the integrating circuit are added to the OR circuit 2, and the OR circuit 2 has a constant threshold level So for the input.
[For the output ■, it is the threshold level S.
An output is produced only when o is exceeded.

Therefore, the output signal of the OR circuit 2 becomes level 1 (corresponding to state A) where the electric field strength is stable and exceeds the electric field detection threshold level, and B where the received electric field strength fluctuates rapidly. Even in the state of , if the frequency exceeds a certain limit, the output of the integrator circuit will continuously exceed the threshold level of the OR circuit 2, and the output signal will also go to a high level accordingly. Become.

The output signal {circle around (2)} of the OR circuit 2 is used as a squelch control signal in a squelch circuit (not shown), and turns off the squelch circuit when it is a no-repel signal, and turns on the squelch circuit when it is at a low level. Therefore, a receiver using a squelch circuit to which the present invention is applied generates continuous received audio output when the received field strength is sufficiently high, and also generates continuous received audio output even when the received field strength fluctuates sharply. It is possible to prevent noise from occurring due to frequent opening and closing of the circuit.

The squelch control circuit of the present invention can also be realized by software using a microcomputer or the like. FIG. 3 shows another embodiment of the present invention, and is a block diagram when realized by software, 1
1 is a squelch control counter, and 12 is a subtraction timer that subtracts a preset constant number with a constant clock. FIG. 4 is a flowchart showing the operation in the embodiment of FIG. 3, and FIG. 5 is a time chart showing the operation of each part, in which (1) is the electric field detection signal and (2) is the subtraction of the subtraction timer. The interval, (3) is the count value of the squelch control counter 11, and (4) is the squelch control signal.

In FIG. 4, at the start of reception, the squelch control counter is cleared (FIG. 4 (1)) and the subtraction timer is set (FIG. 4 (2)). The subtraction timer is set at constant intervals as shown in FIG. 5(2). Next, check whether there is a change in the electric field detection signal (1) (Fig. 4 (3)), and if there is a change, check whether the squelch control counter has reached a predetermined upper limit ( (4) in Fig. 4), and if the upper limit has not been reached, the squelch control counter is incremented by 1 ((5) in Fig. 4). When there is no change in the electric field detection level and when the squelch control counter has reached the upper limit value, the squelch control counter is not incremented.

Next, when the electric field detection level is checked and it is high level, the squelch control signal is set to high level to turn off the squelch circuit, and the electric field detection level is set to the predetermined threshold value. If the squelch circuit is reached, the squelch circuit is turned off in the same way (the fourth
Figure (8)). When the squelch control counter has not reached the predetermined threshold, the squelch control signal is set to low level and the squelch circuit is turned on (see Figure 4).
9)).

Next, check whether the subtraction timer has finished subtracting (QO in Figure 4), and if it has, then check whether the value of the squelch control counter is 0 (Figure 4 (U)). If it is not O, the squelch control counter is decremented by 1 (see Figure 4).
b)), set the subtraction timer again and repeat the same procedure. When the subtraction timer has not finished subtracting, the process repeats from checking the electric field detection level, and when the value of the squelch control counter is 0, it repeats from setting the subtraction timer.

In (3) of FIG. 5, the squelch control counter counts up every time the electric field detection signal changes from high level to low level and low level to high level, and counts down at every subtraction interval of the subtraction timer, so that the electric field detection signal It is explained that at certain times, the count value gradually increases and reaches the upper limit value, and when there is no electric field detection signal, the count value gradually decreases and reaches the lower limit value.

Further, (4) indicates a squelch control signal, which is shown to be at a high level when the electric field detection signal is at a high level and when the count value of the squelch control counter is greater than or equal to a predetermined threshold value.

The squelch control signal obtained in this way (4
) to control a squelch circuit (not shown), as in the embodiment shown in FIG. By generating continuous received audio output even when the squelch circuit is intense, it is possible to prevent noise from occurring due to frequent opening and closing of the squelch circuit.

According to the squelch control circuit of the present invention as described in detail,
Every time an electric field detection signal is generated by detecting that the received electric field strength exceeds a certain threshold, a pulse with a certain width is generated, and this pulse is integrated to generate an output, and this integrated output is constant. When the received electric field strength exceeds the threshold, it is added to the electric field detection signal and the squelch circuit is turned on or off according to this added output, so when the received electric field strength is strong enough, the squelch circuit is turned off continuously and the squelch circuit is turned off normally. Since the squelch circuit is turned off even when the received audio output is generated and the electric field strength fluctuates rapidly, it is possible to reduce noise caused by frequent opening and closing of the squelch circuit. The squelch control circuit of the present invention is particularly suitable for a squelch circuit with a fixed squelch level. Note that the squelch control circuit of the present invention can be easily realized by software in a radio device having a microprocessor unit □tp. Since personal radios and the like are usually equipped with a microprocessor unit, the present invention can be easily implemented using only software.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of one embodiment of the squelch control circuit of the present invention, FIG. 2 is a time chart showing various signals in the circuit of FIG. 1, and FIG. 5 is a diagram showing other embodiments of the squelch control circuit of the present invention. 4 is a flowchart showing the operation of the embodiment of FIG. 6, and FIG. 5 is a time chart showing the operation of each part in FIG. 6. 1°° Monostable multi-vibrator (mono multi), 2... OR circuit, 11... Squelch control counter, 12... Subtraction timer Patent applicant Fujitsu Ten stock % formula % (

Claims (1)

[Claims] In a squelch circuit that detects when the received electric field strength exceeds a certain threshold and generates an electric field detection signal to turn on the received audio output, a pulse of a certain width is generated each time the electric field detection signal is generated. means for generating an output by integrating the pulse, and means for generating an output by adding the integrated output to the electric field detection signal when the integrated output exceeds a certain threshold. , a squelch control circuit characterized in that the squelch circuit is turned on or off depending on the presence or absence of the addition output.