Apparatus for processing video signals and employing phase-locked loop
AssigneeUmax Data Systems Inc.
InventorsShin-Su Wang, Wen-Chin Cheng, Shih-Hsun Lin
Life of this patent
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Abstract
Apparatus for processing video signals and which can be connected with a personal computer for further processing. An analog to digital converter samples and converts input NTSC composite video signal into digital signal for subsequent processing. A phase-locked loop provides sampling clock signal to the ADC, and also ensures accurate sample phase. Based on a theory that human eye is more sensitive to the luminance component of video signals, a double sampling circuit is included which double samples the luminance component of a video signal to improve the overall resolution of an image.
Claims15
A video signal processing apparatus connectable to a personal computer for processing an analog NTSC composite video signal, said apparatus comprising:
- an analog to digital converter for converting said analog NTSC composite video signal into a digital signal represented in a binary form;
- a phase-locked loop connected to said analog to digital converter to form a feed back loop, said phase-locked loop generating a sampling clock signal having a frequency multiple-time of a color burst signal and in phase the color burst signal, and transmitting said sampling clock signal to said analog to digital converter;
- a first-in-first-out buffer coupled to said analog to digital converter for sequentially storing said digital signal converted by said analog to digital converter;
- a frame buffer with a predetermined capacity of multiple frames of digital video signal, connected to said first-in-first-out buffer;
- a control unit for providing said frame buffer and said first-in-first-out buffer timing signal, an output terminal of said control unit connected to the phase-locked loop for controlling the phase of the sampling clock signal;
- and
- a printer port interface connected to said frame buffer for transmission of said video signal and control signal from said video signal processing apparatus to said personal computer.
A phase-locked loop which can be implemented in an apparatus for controlling the sampling phases of video signal and stabling output frequency, said phase-locked loop includes:
- a phase comparator for comparing the phases of two sampling video signals;
- a phase error table generating a phase error signal according to the comparison result of said phase comparator, by looking into a predefined table;
- a low pass filter connected to said phase error table in cascade, reduce the ripple component of said phase-error signal by integration;
- a voltage-controlled oscillator connected to said low pass filter in cascade, to generate a sampling clock signal by voltage change.
Dependencies are inferred from the claim text.