| 摘要 |
SECAM subcarrier demodulator employs a multistage limiter-amplifier to supply two inputs to a signal multiplier, one input being supplied directly and the other input being supplied via a phase shifter which imparts a phase shift of 90 DEG at one of the SECAM subcarrier resting frequencies. Positive feedback is associated with the final amplifier stage of the limiter-amplifier to provide said stage with a hysteresis characteristic ensuring development of a limiter output with a rectangular waveshape having rise and fall times of substantial constancy, independent of input signal amplitude variations. Negative DC feedback from the penultimate amplifier stage to the input amplifier stage of the limiter-amplifier assures desired symmetry of limiting action. Color difference signal output is obtained by low pass filtering of the products of multiplication of the respective signal inputs.
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