Synchrondemodulator fuer modulierte elektrische Hochfrequenzschwingungen

1,037,714. Semi-conductor circuits; stereophonic radio signal receivers. RADIO CORPORATION OF AMERICA. May 29, 1964 [June 19, 1963], No. 22314/64. Headings H3T and H4L. An electronic switching circuit comprises an insulated-gate field-effect transistor having a rectifier coupled between the gate and source electrodes and arranged to provide a low impedance path for signals of a polarity tending to decrease the source-drain resistance of the transistor. Synchronous detectors.-Fig. 4 shows a circuit for demodulating the suppressed carrier signals in a stereophonic radio receiver, under control of pilot carrier signals at 51. Rectifiers 55, 56 become conductive during the respective positive half-cycles of the push-pull pilot signal, so as to charge capacitors 53, 54 in such a way that the insulated-gate field-effect transistors 43, 44 become conductive only during the respective peaks of the pilot signal and hence charge capacitor 64 to the instantaneous value of the modulated wave fed to transformer 60. In Figs. 6, 7 (not shown), the capacitors 53, 54 are replaced by resistors so that the detector operates on average instead of peak values. Fig. 9 (not shown) relates to a synchronous detector similar to one half of Fig. 4 but having the suppressed carrier signal supplied to the source electrode 45. Fig. 10 (not shown) relates to a synchronous detector in which the suppressed carrier signal is fed in parallel to the two drain electrodes of transistors 43, 44, the demodulation being controlled by a half-frequency pilot carrier fed in push-pull to the gate electrodes.