JPH02228882A - Horizontal synchronizing signal generator - Google Patents

Abstract

PURPOSE:To obtain a stable horizontal synchronizing signal for a long period by forming the horizontal synchronizing signal with a color sub carrier as a reference, monitoring the deviation of a phase and correcting the deviation of the phase only when the phase is deviated for more than prescribed quantity. CONSTITUTION:A burst lock PLL circuit 22 separates a color burst signal and outputs a color sub carrier signal synchronized with this color burst signal. Then, the color sub carrier signal is made n-fold in a multiplying circuit 24, made 1/m-fold in a frequency dividing circuit 26. Afterwards, the horizontal synchronizing signal can be obtained by shaping the waveform of the signal in a horizontal synchronizing signal forming circuit 28. A phase comparator circuit 32 compares the phase of the formed horizontal synchronizing signal with the phase of the horizontal synchronizing signal separated from an input video signal by a horizontal synchronizing signal separator circuit 30. When the difference of the phase is deviated for more than the prescribed quantity, a reset signal is outputted. A mask circuit 34 impresses the reset signal to the control terminal of the frequency dividing circuit 26 once a field during the specified period such as a vertical synchronizing period, etc. Thus, the stable horizontal synchronizing signal can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a horizontal synchronization signal generation device that generates a horizontal synchronization signal for a video signal.

[Prior Art] Conventionally, as a configuration for separating a horizontal synchronization signal from a human-powered video signal, there has been a configuration for synchronously separating a horizontal synchronization signal from an input video signal, and a configuration for separating a horizontal synchronization signal from a human-powered video signal.
A known configuration is known in which an L circuit forms a signal phase-synchronized with a horizontal synchronizing signal of a human-powered video signal, and a horizontal synchronizing signal of a predetermined standard is generated from this signal.

FIG. 2 shows a block diagram of the latter conventional example. 10
is a horizontal synchronization signal separation circuit, 12 is a phase comparison circuit, 14 is an oscillator (VCO), 16 is a frequency divider circuit that divides the output of the oscillator 14, 18 is based on the output signal (its frequency) of the frequency divider circuit 16, This is a horizontal synchronization signal forming circuit that generates a horizontal synchronization signal of a predetermined standard. The phase comparison circuit 12 compares the phases of the horizontal synchronization signal from the horizontal synchronization separation circuit 10 and the horizontal synchronization signal from the horizontal synchronization signal forming circuit 18, and
4 changes the oscillation frequency according to the output (phase difference signal) of the phase comparison circuit 12. In this way, it is possible to obtain a horizontal synchronization signal that is phase synchronized with the horizontal synchronization signal of the input video signal.

[Problems to be Solved by the Invention] However, in the former conventional example in which only the horizontal synchronization signal portion is separated from the input video signal, if the input video signal contains noise, it is impossible to completely remove the noise. Therefore, the output horizontal synchronizing signal also contains noise, which has the disadvantage that it is mistakenly recognized as a horizontal synchronizing signal by the subsequent circuit.

In addition, in the latter conventional example, if the brightness of the input video signal suddenly changes, it may be mistaken for a horizontal synchronization signal.
Synchronously separated horizontal synchronizing signal (horizontal synchronizing signal separation circuit 10
The disadvantage is that the period of the horizontal synchronizing signal (output) changes, and the period of the horizontal synchronizing signal formed by the horizontal synchronizing signal forming circuit 18 also changes accordingly.

Therefore, it is an object of the present invention to provide a horizontal synchronizing signal generator free from such drawbacks.

[Means for Solving the Problems] A horizontal synchronizing signal generating device according to the present invention includes a multiplying means for generating a signal n times the frequency of a color subcarrier of a video signal, and an output of the multiplying means for generating a signal with a frequency of n times the frequency of a color subcarrier of a video signal. a frequency dividing means for dividing a frequency; a horizontal synchronizing signal forming means for forming a horizontal synchronizing signal from the output of the frequency dividing means; a horizontal synchronizing signal separating means for separating a horizontal synchronizing signal from the video signal; phase comparison means for outputting a reset signal for resetting the frequency divider when the phase difference between the horizontal synchronization signal outputted by the means and the horizontal synchronization signal outputted by the horizontal synchronization signal separation means is a predetermined amount or more; It is characterized by consisting of.

[Function] The above means forms a horizontal synchronization signal based on the color subcarrier, monitors its phase shift, and corrects the phase shift only when the shift exceeds a predetermined amount, so it is stable for a long time compared to the conventional example. horizontal synchronization signal can be obtained. Furthermore, since the color subcarrier is used as a reference, even if the video signal includes a portion where the brightness changes rapidly, it will not be affected by the change in brightness.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention. In FIG. 1, 20 is a video signal input terminal, 22 is a burst lock PLL circuit for obtaining a color subcarrier frequency signal (hereinafter referred to as a color subcarrier signal) from the video signal of the input terminal 20, and 24 is burst lock PLL
A frequency dividing circuit 26 multiplies the frequency of the color subcarrier signal outputted from the circuit 22 by n; 26 is a frequency dividing circuit 28 which multiplies the output frequency of the multiplier circuit 24 to 17 m in order to obtain a signal of the horizontal synchronization signal frequency; 30 is a horizontal sync signal separation circuit that separates the horizontal sync signal from the input video signal of the input terminal 20; 32 is a horizontal sync signal; A phase comparison circuit that compares the phases of the horizontal synchronization signal formed by the formation circuit 28 and the horizontal synchronization signal separated by the horizontal synchronization signal separation circuit 30, and outputs a reset signal if there is a phase difference of more than a predetermined amount. , 34 are mask circuits that allow the reset signal output from the phase comparator circuit 32 to pass only during a specific period.

Burst lock P is applied to the video signal of input terminal 20.
The LL circuit 22 separates the color burst signal and outputs a color subcarrier signal synchronized with it.

In order to obtain a signal having the frequency of the horizontal synchronizing signal, the multiplier circuit 24 multiplies it by n, and the frequency divider circuit 26 multiplies it by 1/m. For example, N
In the case of TSC signal, if n=4, 1/(4x 2
27.5) = 1/910, and m = 910. By waveform-shaping the output of the frequency dividing circuit 26 by the horizontal synchronizing signal forming circuit 28, a desired horizontal synchronizing signal can be obtained from the output terminal 36.

Further, the phase comparison circuit 32 is connected to the horizontal synchronization signal forming circuit 28.
horizontal synchronization signal (or a signal with the same phase as this)
input terminal 2 by the horizontal synchronization signal separation circuit 30.
It compares the phase of the horizontal synchronization signal separated from the input video signal of 0, and outputs a reset signal when the phase difference deviates by about 2 to 3 cycles or more of the color subcarrier signal. The mask circuit 34 applies the reset signal once per field.
It is applied to the control terminal of the frequency divider circuit 26 during a specific period such as within the vertical synchronization period. As a result, the frequency dividing circuit 26 is reset. That is, when the phase of the output horizontal synchronizing signal deviates by a predetermined amount or more, the frequency dividing circuit 26 is reset, and normally a stable horizontal synchronizing signal can be obtained.

The present invention can be widely applied to cases where the frequency of a color subcarrier and the period of a horizontal synchronization signal have a fixed relationship, such as a video signal output from a camera or a video signal output from a television broadcast receiver. However, the burst lock PLL circuit 22 is not necessary when the color subcarrier signal can be obtained independently of the video signal, such as from a camera output.

[Effects of the Invention] As can be easily understood from the above explanation, according to the present invention, it is possible to obtain a stable horizontal synchronization signal that does not contain noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, and FIG. 2 is a block diagram of the configuration of a conventional example. 10: Horizontal synchronization signal separation circuit 12: Phase comparison circuit 1
4: Oscillator 16: Frequency dividing circuit 18: Horizontal synchronization signal forming circuit 20: Input terminal 22; Burst lock PLL
Circuit 24: Multiplier circuit 26: Frequency divider circuit 28: Horizontal synchronization signal forming circuit 30: Horizontal synchronization signal separation circuit 32
: Phase comparison circuit 34: Mask circuit 36: Output terminal

Claims (2)

[Claims] (1) Multiplication means for generating a signal n times the frequency of the color subcarrier of the video signal, and an output of the multiplication means 1/m.
a horizontal synchronizing signal forming means for forming a horizontal synchronizing signal from the output of the frequency dividing means, a horizontal synchronizing signal separating means for separating the horizontal synchronizing signal from the video signal, and the horizontal synchronizing signal. Phase comparison means for outputting a reset signal for resetting the frequency divider when the phase difference between the horizontal synchronization signal outputted by the forming means and the horizontal synchronization signal outputted by the horizontal synchronization signal separation means is greater than or equal to a predetermined value. A horizontal synchronizing signal generator comprising: (2) The horizontal synchronizing signal generating device according to claim (1), further comprising masking means for supplying the reset signal to the frequency divider only for a specific period.