A variable band-pass filter circuit includes a variable band-pass filter which filters an input signal such as a chrominance signal. An output the variable band-pass filter is phase-compared with a reference signal in a phase comparator. An output of the phase comparator is applied to the variable band-pass...http://www.google.com.au/patents/US5182478?utm_source=gb-gplus-sharePatent US5182478 - Variable band-pass filter circuit
