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A phase-locked loop (PLL) for analog video RGB signal acquisition interface requires precise clock generation from a very noisy and low-frequency horizontal synchronization signal (HSYNC). In such applications, the frequency multiplication ratio is always larger than 800 and can be up to over 2600. The output pixel clock has to be phase aligned to the HSYNC. Otherwise, the displayed image will become blurry. A fast phase tracking all-digital PLL (ADPLL) for video pixel clock generation in a 65 nm CMOS technology is presented in this paper. In the proposed ADPLL, the digital loop filter eliminates the reference clock jitter effects and then the period jitter of the output pixel clock can be reduced. A time-to-digital converter (TDC) and a delta-sigma modulator (DSM) are used to perform the fast phase tracking, and the tracking jitter is controlled at less than one-third of the output pixel clock period. As compared to prior studies, the proposed ADPLL does not require an extra external oscillator to overcome the reference clock jitter effects. Thus, it has a small chip area and low power consumption, and is well-suited to video pixel clock generation applications in 65 nm CMOS process.
Date of Publication: Oct. 2011