Improvements in or relating to circuits for generating a d.c. voltage from recurrentpulses

781,649. Automatic gain control. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Nov. 4, 1954 [Nov. 27, 1953], No. 32940/53. Class 40 (5). In a television A.G.C. circuit the demodulated video'signal (Fig. 2, not shown), is applied to a limiter 1 which removes the greater part of the video component and the resultant waveform is fed in such sense that the synch. pulses are positive-going, to an R.C. circuit 5, 6. The time-constant of the circuit 5, 6 is so chosen that there is produced across the resistance 6 a pair of pulses (Fig. 3, not shown), corresponding to each synch. pulse, the amplitude of each of which is substantially that of the synch. pulse and is independent of the slope of its sides. The negative-going pulses corresponding to the trailing edges of the synch. pulses are applied to a diode peak rectifier 10, the A.G.C. voltage being obtained across its load resistor 11. The limiting level may be varied in accordance with the signal amplitude by applying the A.G.C. bias to the limiter, via lead 14. In a modification, Fig. 4 (not shown), a further valve is interposed between the limiter and the R.C. circuit, being so biased as to pass only the tips of the synch. pulses. The circuit may alternatively be arranged so that the peak rectifier operates on the pulses corresponding to the leading edges of the synch. pulses, while the limiter may be omitted if the amplitude of the synch. pulses is appreciably greater than that of the rest of the signal. Specification 529,319, [Group XL], is referred to.