GB1126477A - Synchronous modulating-demodulating system - Google Patents

Abstract

1,126,477. Amplifiers; phase-sensitive detectors. NORTH AMERICAN AVIATION Inc. 7 April, 1966, No. 15695/66. Headings H3A and H3T. A control system uses a square wave carrier modulated by the control signals and synchronously demodulated by a full-wave rectifier circuit so that the demodulated output is D.C. without the ripple that would be obtained with a sine wave carrier. In Fig. 4, the square wave source 28 (illustrated in Fig. 11, not shown) supplies the carrier to the modulation means and is also coupled as shown to the four FET's 21-24 forming the demodulator so that on one half cycle the input terminal 17 is coupled through 21 to output terminal 18, while output terminal 19 is connected to earth through 24, and on the next half cycle 17 is coupled to 19 and 18 is connected to earth through 22 and 23 respectively. The load 14 may include a differentiating circuit (Fig. 5, not shown) or an integrating circuit (Fig. 6, not shown), or both (Fig. 7, not shown), thereby having the characteristic of a band-pass circuit. One application is to a force balanced inertial sensor (38, Fig. 8, not shown). In another application to an electrohydraulic actuator (Fig. 10, not shown), the input modulated square wave is applied to three channels each comprising an amplifier (34) feeding a demodulator supplying an input of the actuator. There are three feedbacks to each amplifier: an individual feedback, a group feedback common to all three amplifiers, and a signal from a position detector (46).