GB1483824A - High-speed synchronous detector - Google Patents

Abstract

1483824 Synchronous detector circuit GRUNDIG EMV 7 April1975 [31 July 1974] 14223/75 Heading H4L In a high speed synchronous detector circuit for separating a selected one from a plurality of amplitude modulated TDM signals and for use as a colour signal demodulator in a colour TV system, the components of the required signal in the multiplex have superimposed thereon periodic rectangular pulses having an amplitude appropriate to shift the required component into an amplitude range distinct from that of the other components. The resulting components are supplied to a holding circuit comprising a diode 33 and capacitor 34 through an impedance converter 27, 26. The holding circuit has an associated discharge circuit connected across the capacitor 34 comprising resistor 36 in series with a transistor 37 which is controlled by gating pulses having the same periodicity as the rectangular pulses. The value of resistor 36 is such that the voltage on the capacitor after the discharge is lower than any possible value of the resulting signal components. In order to avoid the distortion which may result from the holding and switching operation, the output from the detector circuit, at 35, may be passed to a second similar circuit 41 which is switched (at 138) at a later time than the first, such that the output is held during the switching time in the first circuit.