JPS63149573A - Frequency discrimination circuit - Google Patents

Abstract

PURPOSE:To enhance a space factor, by discriminating two kinds of frequency signals by the combination of two retrigger type monomultivibrators. CONSTITUTION:The first retrigger type monomultivibrator 17 of a reversal time larger than the cycle of the first frequency signal and smaller than the cycle of the second frequency signal and the second retrigger type monomultivibrator 18 of a reversal time larger than the cycle of the second frequency signal are provided. Since the vibrator 18 is triggered by the output of the vibrator 17, the cost reduction and space conservation of a frequency discriminating circuit for discriminating two kinds of frequency signals can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Industrial Application Field The present invention is directed to a frequency discrimination circuit used to discriminate horizontal synchronization frequencies and the like.

(2) Prior Art Recently, TV receivers compatible with new media, personal computers, etc. have come into use. In such a TV receiver, the type of video signal supplied is detected and circuits are switched or displayed. The type of video signal in such a case is generally detected from the horizontal common frequency, and the circuit shown in FIG. 4 may be used.

In FIG. 4, a horizontal synchronizing signal whose type is to be detected is applied to input terminal l. The horizontal synchronization signal is supplied to a retrigger type mono multivibrator 2 and triggers this mono multivibrator 2. The circuit shown in Figure 4 detects which of the two types of horizontal peer signals are 15.75 KHz (period: approximately 0.06 m5 ec) and 24.83 KHz (period: approximately 0.04 m5 e c). circuit, including a capacitor 9 and a resistor 11
The inversion time of the mono-multivibrator 2 determined by the above is set to the middle of both periods (approximately 0.05 m5ec).

Therefore, the 15.75KHz horizontal synchronization signal is input to input terminal 1.
is applied, the Q output of the mono multi vibrator 2 is 15.75 KHz repetition, a positive pulse of mono multi vibrator 920 reversal time is output, and 24
．． When the horizontal synchronizing signal of 83KH2 is applied to the input terminal 1, the Q output of the mono multivibrator 2 is always at the "H" level.

The Q output of this mono-multivibrator 2 is integrated by an integrating circuit consisting of a resistor 12 and a capacitor 10, and then supplied to the base of a transistor 150 via a resistor 13. The resistor 13 and the transistor 15 together with the resistor 14 constitute a comparator 4, which compares whether the output of the integrating circuit 3 is larger or smaller than a reference value (the value obtained by subtracting the base-emitter voltage of the transistor 15 from the power supply voltage). It is carried out.

The output of the comparator 4 is obtained as the collector voltage of the transistor 15, and when the output of the integrating circuit 3 is at "H" level, the collector voltage of the transistor 15 is 14 L 1
1 level, and when the output of the integrating circuit 3 is IT L It level, the collector voltage of the transistor 15 is "H".
level.

The output of the comparator 4 is output as is to the output terminal 6, and is also inverted by the inverter 5 and output to the output terminal 7. As a result, when an output of "'H level" is obtained from the output terminal 6, the horizontal synchronizing signal applied to the input terminal l is discriminated as 15°75K)lz, and the output terminal 7 outputs ttH level. When the level output is obtained, the horizontal synchronizing signal applied to input terminal 1 is 24.
It is discriminated as 83KHz.

(3) Problems to be solved by the invention In the circuit shown in FIG.
In addition, an integrating circuit 3, a comparator 4, and an inverter 5 are required, which increases the number of parts, resulting in a problem of high parts and manufacturing costs. Furthermore, there was also the problem of worsening the space factor due to the large number of parts.

(4) Means for Solving the Problems The present invention has been made in view of the above points, and aims to reduce costs and save space. The first inversion time is larger than the period of the signal and smaller than the period of the second frequency signal.
A retrigger type mono multivibrator and a second retrigger type mono multivibrator with an inversion time larger than the period of the second frequency signal are provided, and the output of the first retrigger type mono multivibrator is used to generate a second retrigger type mono multivibrator. The device is configured to trigger a vibrator.

(5) Effect In this configuration, only the combination of two retrigger type mono-multivibrators acts to discriminate between two types of frequency signals.

(6) Examples Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a block diagram showing one embodiment of a frequency discrimination circuit according to the present invention.

In FIG. 1, a horizontal synchronizing signal whose type is to be detected is applied to an input terminal l. The horizontal synchronization signal is supplied to a retrigger type mono multivibrator 17,
This mono multivibrator 17 is triggered. 1st
The circuit shown in the figure has a horizontal synchronization signal of 15.75KHz (
Zhou! ! 11 Tl is approximately 0°06 msec)
and 24.83KH2 (around! IJI T 2 is about 0.04
m5ec), and the inversion time Ta of the mono-multivibrator 17 determined by the capacitor 19 and resistor 21 is the middle of both periods (approximately 0.05 m5ec, therefore T2 <Ta<
TI).

The Ql output of the mono multivibrator 17 is supplied to the mono multivibrator 18. The capacitor 20 and resistor 22 that determine the inversion time Tb of the mono multivibrator 18 are set so that the period is larger than the period of the horizontal synchronizing signal (period TI = 0.06 m5ec) of 15.75KH2, therefore, T2 < Ta < TI < Tb. It is set to be. Q2 output and Q of mono multivibrator 18
Two outputs are output from output terminal 6 and output terminal 7, respectively.

Next, the operation will be explained with reference to FIGS. 2 and 3.

Connect input terminal 1 to 15°75KH as shown in Figure 2(a).
When the horizontal synchronizing signal A of z (period T1 is about 0.06 m5ec) is applied, the Q1 output of the mono multivibrator 17 becomes as shown in FIG. 2(b). The Q2 output and Q2 output of the mono multivibrator 18, which are triggered by the rising edge of the Ql ratio output (Fig. 2 (C)) of the mono multivibrator 17, are as shown in Fig. 2 (d) and Fig. 2 (e), respectively. become. That is, an output of °'H" level is obtained from the output terminal 6, and an output of "L" is obtained from the output terminal 7.
II level output can be obtained. From this, the horizontal synchronization signal applied to input terminal l is 15°75KHz.
It is distinguished as

In addition, the input terminal l has a 24.8
When a horizontal synchronizing signal of 3 KHz (period IJIT2 is about 0.04 m5ec) is applied, the Q1 output of the mono multivibrator 17 becomes as shown in FIG. 3(b). Figure 3: Ql ratio output of mono multivibrator 17 (C
)) The Q2 output and Q2 output of the mono multivibrator 18, which are triggered by the rising edge of become.

That is, an "L" level output is obtained from the output terminal 6, and an "H" level output is obtained from the output terminal 7. From this, the horizontal synchronizing signal applied to the input terminal l is determined to be 24.83 KHz.

Although the present invention has been described above using examples, various modifications are possible according to the technical idea of the present invention. For example, in the embodiment, the case where the horizontal synchronizing signal applied to the input terminal l is 15.75 KHz and 24°83 KHz is explained, but if the horizontal synchronizing signal is applied to the input terminal l,
Of course, a frequency other than KHz or 24°83KH2 may be used.

(7) Effects of the Invention As explained above, the present invention provides a first retrigger type mono multivibrator with an inversion time larger than the period of the first frequency signal and smaller than the period of the second frequency signal. , a second retrigger type mono multivibrator having an inversion time larger than the period of the second frequency signal, and the second retrigger type mono multivibrator is triggered by the output of the first retrigger type mono multivibrator. With this configuration, it is possible to reduce the cost and space of the frequency discrimination circuit that discriminates between two types of frequency signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the frequency discrimination circuit according to the present invention, FIG. 2 is a waveform diagram explaining the operation of the frequency discrimination circuit according to the present invention, and FIG. 3 is a frequency discrimination circuit according to the present invention. FIG. 4 is a block diagram showing a conventional frequency discrimination circuit. 17φ...Mono multivibrator 18-...Mono multivibrator 19...Capacitor 20...Capacitor 21...Resistor 22...Resistance Patent applicant NEC Home Electronics Co., Ltd. Agent Patent attorney Yama 1) Takeshi Tree 1st Figure 1d 4th Circle Figure 2 Figure 3 (C) ((1)
``Bi'ro 2

Claims (1)

[Claims] In a frequency discrimination circuit that discriminates between two types of frequency signals, first and second, a first retrigger type mono-multivibrator having an inversion time larger than the period of the first frequency signal and smaller than the period of the second frequency signal. and a second retrigger type mono multivibrator with an inversion time larger than the period of the second frequency signal, and the second retrigger type mono multivibrator is controlled by the output of the first retrigger type mono multivibrator.
A frequency discrimination circuit characterized by triggering a retrigger type mono multivibrator.