SECAM Chroma demodulator circuit

In apparatus for recovering color-difference signal information from a chrominance signal encoded in SECAM fashion but undesirably subject to variations in amplitude over a given range, the combination of:

• a multi-stage limiter-amplifier responsive to said chrominance signal;
• a phase-shifting network having an input terminal for imparting to a signal supplied to said input terminal a phase shift of a frequency-dependent magnitude, said phase-shift magnitude being substantially 90.degree. when the frequency of a signal supplied to said input terminal corresponds to a SECAM color subcarrier resting frequency;
• means for applying the output of said limiter-amplifier to said network input terminal;
• a signal multiplier, having a pair of input terminals and an output terminal, for developing at said output terminal the products of multiplication of respective signals applied to said pair of input terminals;
• means for applying the output of said limiter-amplifier to one of said signal multiplier input terminals;
• means for applying the output of said phase-shifting network to the other of said signal multiplier input terminals;
• and
• low pass filter means coupled to said signal multiplier output terminal for developing a color-difference signal output;
• wherein one of the stages of said multi-stage limiter-amplifier includes means for providing said one amplifier stage with a hysteresis characteristic of a form ensuring development by said limiter-amplifier of an output signal with a rectangular wave-shape possessing rise and fall times which are substantially independent of amplitude variations of the signal input to said limiter-amplifier over said given range.