Horizontal phase-locked loop for video decoder

摘要

A phase-locked loop is provided which is operable to lock the sampling clock (pixel clock) to the incoming horizontal sync pulse contained within composite video information. Two modes of operation, coarse lock mode and fine lock mode, are used in controlling the phase-locked loop. In the coarse lock mode, coarse corrections are made to a horizontal discrete time oscillator so that a fast lock may be achieve using the fine lock mode. Coarse corrections are based on a normalized sum of weighted pixels collected within a narrow gate window. Lock is achieved when the falling edge is centered within the window.