Abstract: A digital pulse filtering circuit for filtering out pulses of specific pulse widths in a composite signal is provided. The digital pulse filtering circuit includes a sampling circuit for sampling the input composite signal based on a periodic clock signal to thereby generate a plurality of sampled signals of the input composite signal. In response to these sampled signals, a detection circuit outputs a low-frequency composite signal which is a filtered version of the input composite signal. The digital pulse filtering circuit is completely based on digital circuitry which can be built in integrated circuits. The cutoff frequency of the digital pulse filtering circuit is dependent on the frequency of the clock signal, which is very easy and accurate to adjust.

Abstract: A digital pulse filtering circuit for processing composite sync signals is provided. The digital pulse filtering circuit can determine the polarity of an input composite sync signal composed of a horizontal sync signal and a vertical sync signal. The horizontal sync signal is a first periodic pulse train having a first pulse width, while the vertical sync signal is a second periodic pulse train having a second pulse width. The digital pulse filtering circuit includes a horizontal sync filter for filtering out all pulses in the input composite sync signal that have a pulse width less than the pulse width of the horizontal sync signal; and a vertical sync filter, coupled to receive the output of said horizontal sync filter, for filtering out all pulses in the output of said horizontal sync filter that have a pulse width less than the pulse width of the vertical sync signal. The output of said indicating the polarity of the input composite sync signal.