Synchronous detector

#1. Field of the Invention

#The present invention relates to a synchronous detector for detecting a synchronization signal from a composite signal including a synchronization signal, a luminance signal and a chrominance signal, a luminance signal including a synchronization signal and so on and, particularly, to a synchronous detector for detecting a synchronization signal stably.

#2. Description of Related Art

#The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is a block diagram showing a synchronous detector according to a first embodiment of the present invention;

#FIG. 2 is a pattern diagram showing signal waveforms of a video signal Din, a limited signal D1, a first filter circuit output signal D2, and a horizontal synchronization signal HS;

#The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposed.

#FIG. 1 is a block diagram showing a synchronous detector according to a first embodiment of the present invention. The synchronous detector 10 includes a horizontal synchronization level detector 11, a synchronization signal extractor 12 and a synchronous detection section. The horizontal synchronization level detector 11 detects a horizontal synchronization detection level HL, which is described later, from an input signal. The synchronization signal extractor 12 receives the input signal and the horizontal synchronization detection level HL and generates a limited signal D1. The synchronous detection section detects a horizontal synchronization signal from the limited signal D1. The synchronous detection section includes a first filter circuit 13 and a horizontal synchronous separator 14. The first filter circuit 13 removes high frequency component of the limited signal D1. The horizontal synchronous separator 14 separates the horizontal synchronization signal from the signal D2 on which the LPF processing is performed by the first filter 13 and outputs a horizontal synchronization signal HS.

#Each block is described in detail below. The input signal is a signal containing a synchronization signal, such as a composite signal composed of a luminance signal and a chrominance signal (color signal) superimposed with a synchronization signal, a luminance signal containing a synchronization signal and so on. This embodiment refers to an input signal as a video signal Din. The video signal Din is input to the horizontal synchronization level detector 11 and the synchronization signal extractor 12.