Demodulator system including a tunable discriminator suitable for use in a secam television receiver

Abstract

A demodulating system to be utilized in Secam television receivers for deriving the R-Y and B-Y chrominance information signals from the frequency modulated Secam RF subcarrier frequencies without the necessity for precise and stable tuned circuits. The demodulating system includes a single discriminator having an electronically tunable center frequency, a remodulator, for producing a reference frequency amplitude modulated by the chrominance information signals which are supplied to a commutator as known, and a feedback circuit coupled between the discriminator and remodulator. The discriminator is selectively tuned to a reference center frequency during each picture line clamp period to produce a zero level output signal. During the chrominance information portion of each line, the center frequency of the discriminator is alternately offset by first and second control signals to center frequencies coinciding with the two reference frequencies to produce a zero output level whenever the Secam signals are at the respective RF subcarrier frequencies. The feedback circuit ensures that the zero output levels obtained during the information carrying portion of each line is identical with the zero output level set during the clamp period.

Dependencies are inferred from the claim text.