| 摘要 |
A circuit arrangement for demodulating the chrominance signal portion of a color television signal in an apparatus for receiving at least said color television signal is described. The chrominance signal to be demodulated is of the type that is coded according to the ISA (Identify Suppressing Alternately) system, i.e. the chromatic information modulates in amplitude by carrier suppression a subcarrier along two axes in quadrature, one of the axes being switched 180 DEG each line, a single reference signal of constant phase being inserted only every second line and serving as a reference signal for the demodulation of said subcarrier and as an identification signal for the switching. According to the invention, an electronic gate is provided which opens during part of every second line scanning period to allow the passage of the single reference signal to a passive crystal filter. An amplitude detector circuit receives a plurality of oscillations at subcarrier frequency from the filter and supplies an identification signal for a switching voltage generator which controls the electronic gate and synchronizes a change-over switch which operates at line frequency for obtaining the demodulated chromatic information.
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