Abstract: A band-pass filter system comprises a band-pass filter, and a frequency band controller for controlling a frequency band of the band-pass filter by generating a corresponding up pulse voltage and a down pulse voltage according to a pre-controlled center frequency obtained from an output frequency of the band-pass filter to produce a control frequency for obtaining a desired center frequency of the band-pass filter.

Abstract: A vertical synchronous signal separation circuit is disclosed wherein the circuit includes a vertical synchronous pulse removal circuit for delaying original horizontal and vertical synchronous signals separated from a composite video signal by a predetermined time period in response to a reference clock signal and logically combining the original horizontal and vertical synchronous signals with the delayed horizontal and vertical synchronous signals to remove vertical synchronous pulses therefrom, a clock generator for logically combining an output signal from the vertical synchronous pulse removal circuit with the reference clock signal to generate a clock signal, an edge detector for detecting edges of the output signal from the vertical synchronous pulse removal circuit and outputting the detected edges as a reset signal, and a vertical synchronous signal extractor for extracting a stable vertical synchronous signal from the original horizontal and vertical synchronous signals in response to the clock sig