The poly-phase shift filter for a time-shared DAC in a digital convergence system

A digital CRT convergence control system usually employs an independent digital-to-analog converter (DAC) for each Red, Green and Blue signal. If the DAC is time-shared among R, G and B signals, the complexity and the size of hardware can be much reduced. However, sharing of the DAC introduces a time-delay among control signals, resulting in a misconvergence and a poor picture quality in projection TV. This paper proposes a digital convergence system that employs poly-phase shift filters to eliminate the time-delay problem in a time-shared DAC. The proposed system got a patent and has been successfully implemented in ASIC, and is currently used in commercial production of projection TV.