JPS6037813A - Timing signal extracting circuit - Google Patents

Abstract

PURPOSE:To restore a complete timing signal from a missing input timing signal by providing a frequency divider outputting a signal having the same frequency as that of the input timing signal and synchronizing the frequency-divider with the input timing signal. CONSTITUTION:An output of a fixed oscillator 17 oscillated in a frequency being an integral number of multiple of the frequency of the timing signal is frequency-divided by a frequency divider 18. The frequency divider 18 is a frequency divider being resettable and outputting a signal having a frequency the same as the frequency of the timing signal and is reset by the timing signal D inputted from an input terminal 1. Then a noise eliminating circuit 14 eliminates a noise component 9 included in the input timing signal C. Thus, even if the input timing signal C has a missing 10, the complete timing signal E is obtained from an output terminal 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a circuit for extracting only a timing signal from an input timing signal that includes noise and is susceptible to deterioration.
The present invention relates to a timing signal extraction circuit that can eliminate noise, correct timing signal dropout, and generate an internal timing signal even when the timing signal is dropped.

Conventionally, from timing signals that contain noise and are prone to deterioration,
As a circuit for extracting only the timing signal, a noise removal circuit composed of a bandpass filter, a low-pass filter, a humpator, a waveform shaping circuit, etc. has been used.

Figure 1 shows an example of a noise removal circuit. 01 is a timing signal input terminal, 2 is a low-pass filter composed of a resistor 3 and a capacitor 4, and 5 is a low-pass filter whose output signal is larger than a preset amplitude value. A comparator that inverts the output depending on whether the output is positive or negative, 6 is a comparator 5
The output (Ft) is a waveform shaping circuit that shapes the waveform and generates a rectangular wave, and 7 is a timing signal output terminal from which noise has been removed.

Note that any known circuit using a differential amplifier or an O-MOS inverter threshold level can be used as the comparator.

When the timing signal input from the timing signal input terminal 1 is input to the low-pass filter 2, the amplitude of the noise included in the timing signal is attenuated, and the amplitude is reduced to the threshold level of the next stage comparator 5, that is, the preset amplitude value. Therefore, a timing signal with noise removed can be taken out from the timing signal output terminal 7.

This situation is shown in FIG.

Figure 2-B is the timing signal input from the timing signal input terminal 1, 8 is the true timing signal, 9 is the mixed noise, 10 is the omission of the timing signal, and Figure 2-B is the timing signal. This is a timing signal output from the signal output terminal 7. As described above, it is possible to remove the noise contained in the timing signal by using the conventional noise removal circuit. However, as shown in FIG. 2, there is no compensation for timing signal dropout. FIG. 2 - Human timing signal dropout 10
It also appears as a dropout in the output signal in Figure B. Originally,
Timing signal dropout can be regarded as the superimposition of noise of opposite polarity on the timing signal, and under conditions where noise mixing occurs, the phenomenon of timing signal dropout almost always occurs. However, while in the past, only the incorporation of noise has been compensated for using various noise removal circuits, no compensation has been made for the dropout of the timing signal.

As a specific example, an example of a horizontal synchronization circuit of a conventional portable television receiver is shown in FIG. 11 is a composite video signal input terminal, 12 is a synchronization separation circuit that separates the composite synchronization signal from the composite video signal, 16 is a horizontal synchronization signal separation circuit that separates the horizontal synchronization signal from the composite synchronization signal, and 14 is the output of the horizontal synchronization signal separation circuit. Noise removal circuit for removing noise included in 15
1 is a horizontal AFO circuit, and 16 is a horizontal AFO circuit output terminal.

Portable television receivers are often used in moving bodies such as trains and cars rather than in a stationary state, and compared to stationary television receivers, they are more susceptible to sudden changes in electric field strength. T75 wave 11 wave sound 1f sound is occurring frequently. Therefore, the horizontal synchronizing signal obtained by the horizontal synchronizing signal separation circuit of a portable television receiver contains noise or is much more likely to drop out than that of a stationary television receiver. Moreover, there are also periods when noise is mixed in and periods when the horizontal synchronization signal is dropped;
Television receivers for j''''t'I have a wide range of uses, from short-term to long-term use.

In the horizontal synchronization circuit shown in FIG. 6, the noise mixed into the horizontal synchronization signal can be removed by the noise removal circuit 14, and the horizontal AFO circuit 15 operates stably against this noise. However, since there is no compensation for horizontal synchronization signal dropout, which occurs frequently as well as noise incorporation, nothing is input to the horizontal AFO circuit 15, and therefore the horizontal synchronization signal is The internal oscillator that is left in the AFO circuit 15 has the drawback that it oscillates at a frequency lower than the frequency of the horizontal synchronizing signal, and the image is frequently distorted.
1\S/lp The promise of Kazuto is to provide a circuit that generates an internal timing signal that maintains the state before the timing signal was dropped even if the timing signal was dropped. The present invention will be described in detail below based on Examples.

FIG. 4 is a block diagram of the timing signal extraction circuit of the present invention, in which 1 is a timing signal input terminal, 14 is a noise removal circuit for removing noise mixed in the timing signal, 17 is composed of a crystal oscillator, etc. A fixed oscillator that oscillates at a frequency that is an integral multiple of the frequency of the timing signal. 18 is a resettable frequency divider circuit that divides the output signal of the fixed oscillator 17 and outputs a signal with the same frequency as the timing signal. 19 is a frequency divider circuit. 18 signal output terminals. Also, FIG. 5 is a waveform diagram of each part of the block diagram shown in FIG. 4. FIG. 5-C is a timing signal input from the timing signal output terminal 1, 8 is a true timing signal, and 9 is The mixed noise 10 represents a dropout of the timing signal, and when this signal is input to the noise removal circuit 14, as already mentioned, the noise 19 is removed, and the dropout 10 of the timing signal is the 1st noise that is not compensated for at all. A signal of 5jJ-D is obtained. On the other hand, the frequency dividing circuit 1B frequency-divides the output signal of the fixed oscillator 17 and outputs a signal with the same frequency as the timing signal. It outputs a frequency signal. Therefore, by resetting the frequency dividing circuit 18 with the timing signal after noise removal as shown in FIG. Not only can this be prevented, but even if the timing signal is dropped, the frequency divider circuit 18 outputs a signal with the same frequency as the timing signal, so the internal timing signal 20 shown in FIG. can be output.

Next, as a specific example of this circuit, a horizontal synchronization circuit for a portable television receiver is shown in FIG. 11 is a composite video signal input terminal, 12 is a synchronization separation circuit that separates the composite synchronization signal from the composite video signal, 13 is a horizontal synchronization signal separation circuit that separates the horizontal synchronization signal from the composite synchronization signal, and 14 is a horizontal synchronization signal dropout 1. A noise removal circuit 17 removes noise contained in the circuit output, and 17 is a fixed oscillation circuit composed of a crystal oscillator, etc., which oscillates at a frequency that is an integral multiple of the frequency of the horizontal synchronization signal.
18 is a frequency dividing circuit that can divide the output signal of the fixed oscillator 17 and output a signal of the same frequency as the horizontal synchronization signal, 15 is a horizontal AFO circuit, and 16 is a horizontal AFO circuit.
In the horizontal synchronous circuit shown in Figure 6, which is the circuit output terminal,
The noise mixed in the horizontal synchronization signal can be removed by the noise removal circuit 14, similar to the horizontal synchronization circuit shown in FIG.
By resetting 8, there will be no reset malfunction due to noise, and the horizontal synchronizing signal and the output signal of the frequency dividing circuit 18 can be synchronized.

Therefore, similar to the horizontal M circuit shown in FIG. 3, it is expected that the horizontal AFO circuit 15 will operate stably against the introduction of noise, and the screen will be stable. Furthermore, since the frequency divider circuit 18 divides the output signal of the fixed oscillator 17 and outputs a signal with the same frequency as the horizontal synchronization signal, when the horizontal synchronization signal is dropped, the state before the drop is maintained and the internal horizontal A synchronization signal can be output, so even when the horizontal synchronization signal is dropped, the horizontal A1! The output signal of the frequency dividing circuit 18 synchronized with the horizontal synchronizing signal is inputted to the 'C circuit 15, and even if the horizontal synchronizing signal is dropped, the horizontal AFO circuit 15 operates stably and the screen is stable. As described above, when the circuit of the present invention is implemented in the horizontal synchronization circuit of a portable television receiver, a more stable screen can be obtained than in the conventional portable television receiver.

In the circuit of the present invention, if the oscillation frequency of the fixed oscillator changes due to temperature drift or the like, the frequency of the internal timing signal generated when the timing signal drops does not match the frequency of the timing signal. but,
Taking the horizontal synchronization circuit of a mobile television receiver as an example,
Even if the frequency of the internal horizontal synchronization signal generated when the horizontal synchronization signal is dropped is slightly different from the frequency of the horizontal synchronization signal, if the circuit configuration shown in Figure 6 is used, the horizontal A when the horizontal synchronization signal is dropped
The drift of the internal oscillation frequency within the FO circuit is smaller than when no input is input to the horizontal AFO circuit, as in the conventional circuit configuration shown in Figure 3, and the response when the horizontal synchronization signal is input again is also good. Become.

Therefore, even if the oscillation frequency of the fixed oscillator changes due to temperature drift 1, etc., the circuit of the present invention is effective.
It has great significance.

As described above, according to the present invention, in a circuit that extracts only a timing signal from an input timing signal that includes noise and is prone to deterioration, it is possible to not only remove noise, but also maintain the state before the timing signal is dropped even when the timing signal is dropped. It is possible to generate an internal timing signal that maintains the same, and it is possible to provide a timing signal extraction circuit and a circuit that is particularly suitable for a horizontal synchronization circuit of a portable television receiver.

[Brief explanation of drawings]

Figure 1 is a conventional example of a noise removal circuit, Figure 2 is a waveform diagram of the circuit in Figure 1, Figure 3 is a diagram showing an example of a conventional horizontal synchronization circuit, and Figure 4 is a timing signal extraction method of the present invention. FIG. 5 is a block diagram of the circuit, FIG. 5 is a waveform diagram of each part of FIG. 4, and FIG. 6 is a diagram showing an embodiment of a horizontal synchronization circuit employing the present invention. 1 is a timing signal input terminal, 2 is a low-pass filter, 3 is a resistor, 4 is a capacitor, 5 is a comparator, 6 is a waveform shaping circuit, 7 is a timing signal output terminal, 8 is a true timing signal, 9 is a noise, 10 is timing signal dropout, 11
is a composite video signal input terminal, 12 is a synchronization separation circuit, 13 is a horizontal synchronization signal separation circuit, 14 is a noise removal circuit, 15 is a horizontal AFC circuit, 16 is a horizontal AFO circuit output terminal, 1 is a fixed oscillator, and 18 is a separation circuit. 19 is a signal output terminal of the frequency dividing circuit, and 20 is an internal timing signal. Applicant: Suwa Seikosha Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] A fixed oscillator that oscillates at a frequency that is an integral multiple of the frequency of an input timing signal, a resettable frequency divider circuit that divides the output signal of the fixed oscillator and outputs a signal with the same frequency as the input timing signal, and an input timing signal. The frequency dividing circuit is reset by the output signal of the noise eliminating circuit and has means for synchronizing the input timing signal with the output signal of the frequency dividing circuit. Features a timing signal extraction circuit.