JPH0773166B2 - Transient elimination circuit for pulse count detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a pulse count detector used when demodulating an FM signal, and more specifically to a low frequency circuit of the pulse count detector. This is for a circuit that eliminates the transient phenomenon that occurs in.

(B) Conventional Technique Next, FIG. 3 shows a circuit diagram of a pulse count detector according to the conventional technique.

In FIG. 3, 1 is a limiter, 2 is a monostable multivibrator (hereinafter referred to as monomulti), 3 is a low-pass filter (hereinafter referred to as LPF), 4 is a DC cut capacitor, 5 is an amplifier, 11 Is the intermediate frequency input terminal, 12
Is a low frequency output terminal.

The pulse count detector is described in "Radio Technology", April 1979, "About pulse count detector".

Next, the operation of FIG. 3 will be described with reference to FIG. In FIG. 3, the intermediate frequency of the input terminal 11 is made constant in amplitude by the limiter 1 and pulse-counted by the monomulti 2. Fourth
FIG. 9A is an output waveform diagram of the monomulti 2. For example, the fourth
The intermediate frequency in the figure is 200kHz, and the pulses are at intervals of 1: 4,
The pulse width is constant and the pulse amplitude is 5V.

The output of the monomulti 2 passes through the LPF 3 to remove the high frequency component, and the low frequency output is taken out from the terminal 12. For example, LPF3
Pass frequency is 15kHz, FM modulation frequency is 30Hz to 15kHz.

FIG. 4A is an output waveform diagram of the LPF 3, and is a waveform diagram of the superimposed DC voltage. In the pulse count detector, as shown in FIG. 4 (a), when the intermediate frequency enters, the DC voltage is superimposed on the demodulated signal and comes out. Therefore, in order to amplify the low frequency signal to the required level, the capacitor 4 for cutting the DC voltage is required.

The output of LPF3 is input to the capacitor 4, cuts the DC voltage, and is input to the amplifier 5. FIG. 4C is an input waveform diagram of the amplifier 5. As shown in FIG. 4C, at the output of the capacitor 4, a transient phenomenon occurs at the moment when the intermediate frequency is entered.

In recent wireless communication, control signals are sent to identify each other and control channels. This control signal is sent in a short time until the transmission output of the FM transmitter rises and the modulation by the data starts. Therefore, in the case of demodulating a signal including this control signal, if an attempt is made to amplify a low frequency signal to a required level, in the configuration of FIG. 3, a capacitor for cutting a DC voltage is used as shown in FIG. Transients occur, during transients,
There is a problem that it cannot be demodulated.

(C) Object of the Invention The present invention provides a transient phenomenon elimination circuit for eliminating a transient phenomenon as shown in FIG. 4C by adding a mono-multi, a voltage dividing circuit and a differential amplifier to a conventional pulse count detector. To aim.

(D) Embodiment of the Invention Next, FIG. 1 shows a block diagram of an embodiment according to the present invention.
In FIG. 1, 6 is a monomulti, 7 and 8 are resistors, 9 is a differential amplifier, and other parts are the same as in FIG. That is, FIG. 1 is obtained by adding the monomulti 6, the resistors 7 and 8, and the differential amplifier 9 to FIG.

In FIG. 1, the mono-multi 6 receives the output of the mono-multi 2 and is connected so as to be at a high level by the output of the mono-multi 2. For example, the operating frequency of Mono Multi 2 is 200kHz
If so, the operating frequency of the monomulti 6 is set to 15 kHz.

The resistors 7 and 8 form a voltage dividing circuit, and the output of the monomulti 6 is used as an input. The differential amplifier 9 is LPF3
Is used as the first input and the output of the voltage dividing circuit is used as the second input to output to the capacitor 4 and amplified by the amplifier 5.

Next, the operation of FIG. 1 will be described with reference to the waveform chart of FIG.

Figure 2 (a) shows the output waveform of Mono Multi 2 and Figure 2 (i) shows LPF3.
2 is an output waveform diagram of FIG. 2A and FIG. 4A and FIG. 4A are the same. For example, if the output voltage of the 2nd is 5V,
The DC voltage in Fig. 2B is about 1.25V. The rise time in FIG. 2A is about 0.1 ms.

FIG. 2C is an output waveform diagram of the voltage dividing circuit. Mono Multi 6
2 becomes high level when the mono-multi 2 outputs as shown in FIG. 2A, and since the operating frequency is slower than that of the mono-multi 2, it keeps the high level. The output voltage of the mono-multi 6 is adjusted by the voltage dividing circuit composed of the resistors 7 and 8 to be the same as the DC voltage shown in FIG.

FIG. 2D is an output waveform diagram of the differential amplifier 9. FIG. 2D is a waveform diagram showing the difference between FIGS. 2A and 2C, and the DC voltage is theoretically 0V. FIG. 2E is an output waveform diagram of the amplifier 5. As shown in FIG. 2D, the DC voltage input to the capacitor 4 is sufficiently suppressed, so that the transient phenomenon is eliminated.

Although the mono-multi 6 is connected to the output of the mono-multi 2 in FIG. 1, the mono-multi 6 may be connected to the input side of the mono-multi 2.

(E) Effect of the Invention According to the present invention, in the conventional pulse count detector, the mono-multi 6 receives the output of the mono-multi 2 as input, and is connected so that the output of the mono-multi 2 becomes high level. Adjust the output of Multi 6 with a voltage divider composed of resistors 7 and 8 to make it the same as the output voltage of LPF3, input the output of LPF3 and the output of the voltage divider to a differential amplifier, and use a pulse count detector. Since the DC voltage which is superposed on the demodulated signal of and is output is canceled, the transient phenomenon can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment according to the present invention, and FIG.
FIG. 3 is a waveform diagram of FIG. 3, FIG. 3 is a circuit diagram of a pulse count detector according to the prior art, and FIG. 4 is a waveform diagram of FIG. 1 ... Limiter, 2 ... Monostable multivibrator (monomulti), 3 ... Low-pass filter (LP
F) 4 ... Capacitor, 5 ... Amplifier, 6 ... Monomulti, 7 ... Resistor, 8 ... Resistor, 9 ... Differential amplifier.

Claims (2)

[Claims] 1. A limiter (1) for keeping the amplitude of an intermediate frequency constant, a first monostable multivibrator (2) for counting pulses by using an output of the limiter (1) as an input, and a first monostable. A low-pass filter (3) that receives the output of the multivibrator (2) and removes harmonic components, and a capacitor (4) that receives the output of the low-pass filter (3) and cuts the DC voltage.
In a pulse count detector having an amplifier (5) which receives the output of a capacitor (4) and amplifies it to a required level, the output of the first monostable multivibrator (2) is input to a high level and maintained. A second monostable multivibrator (6), and a voltage dividing circuit for dividing the output voltage of the second monostable multivibrator (6) and adjusting the output voltage of the low-pass filter (3) to the same level, A transient elimination circuit for a pulse count detector, characterized in that a differential amplifier (9) is provided, which receives the output of the low-pass filter (3) and the output of the voltage dividing circuit and inputs it to a capacitor (4). 2. The transient elimination of the pulse count detector according to claim 1, wherein the second monostable multivibrator (6) receives the output of the limiter (1) and becomes a high level. circuit.