PCM Signal extracting circuit

Abstract

A PCM signal extracting circuit comprises a highpass filter for separating a PCM signal, of a type not including a DC component, inserted between horizontal synchronizing signals within a predetermined interval of a composite video signal or a signal based on the composite video signal, and for obtaining an average DC level of the horizontal synchronizing signal and the PCM signal, an attenuation circuit for attenuating an output signal of the highpass filter by a predetermined quantity according to the modulation factor of the PCM signal, a holding circuit for holding a peak value, at the opposite side from the horizontal synchronizing signal, of the signal attenuated by the attenuation circuit, and a level comparing circuit for comparing the levels of output signals of the highpass filter and the holding circuit, and extracting a signal obtained by slicing the output signal of the highpass filter by the level of the output signal of the holding circuit. The attenuation circuit attenuates the PCM signal so that the level of the peak value, at the opposite side from the horizontal synchronizing signal, of the attenuated PCM signal, is equal to a level shifted towards a side opposite from the horizontal synchronizing signal by kx% from an average DC level of the PCM signal before attenuation, where k is a constant, and a distance between the average DC level of the PCM signal and the peak value of the PCM signal at the opposite side from the horizontal synchronizing signal is designated by x% where the distance between the pedestal of the horizontal synchronizing signal and the white peak level is expressed as 100%.

Dependencies are inferred from the claim text.