GB915604A - Improvements in systems for amplifying and demodulating modulated signals - Google Patents

Abstract

915,604. Transistor amplifying circuits. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Feb. 10, 1961 [Feb. 17, 1960], No. 5127/61. Class 40 (6). [Also in Group XXXV] In a system for amplifying an error signal of the type e = E sin (wt+## wherein # = 0 or 1 and wherein E represents the magnitude of the error and e the sign of the error, an auxiliary voltage U cos wt is applied with the error signal to a modulation converter which delivers a substantially rectangular phase-modulated voltage wave, the phase of which with respect to voltage sin wt carries the information E and #; the rectangular waveform is amplified by a transistor circuit the output of which is applied to a phase detector circuit. As applied to a servo system, Fig. 2, a device 70 to be controlled by a motor 60 includes an error voltage generator which error voltage appears across terminals 71 and 72. An auxiliary voltage U cos wt, derived from a source 63 and an RC circuit 67, 69, and the error signal form the input to a modulator comprising common-emitter connected transistors 11 and 12, the arrangement being such that the modulator delivers a substantially rectangular wave from whose zero value is shifted by # - # and - # with respect to voltage sin wt. It can be shown that tan # = E/U for # = 0 and - E/U for # = 1; the angle # thus represents the information contained in the original error signal. The rectangular wave output from the transistors 11, 12 is applied to an amplifier comprising further transistors 31, 32 which operate as switches and which are connected to a demodulator arrangement comprising a transformer 42 and a diode bridge controlled by a voltage from source 63 of angular frequency #, the output from the demodulator having a D.C. component proportional to cos #. The torque on the D.C. motor 60 the rotor of which is connected to the demodulator is therefore proportional in magnitude to and of the same sign as the original error, and the motor therefore drives the device 70 in a sense to correct the error.