GB1204215A - Improvements in or relating to transistor modulator circuits - Google Patents

Abstract

1,204,215. Amplitude modulators; transistor amplifiers. MINISTER OF TECHNOLOGY. 7 Jan., 1969 [9 Jan., 1968], No. 1343/68. Headings H3R and H3T. A modulator comprises transistors Q1, Q2, Q3 of the same conductivity type, with the carrier applied to the base of Q3, and antiphase modulation signals applied to the bases of Q1, Q2, the carrier signal range embracing the ranges of the signals at the bases of Q1, Q2: When the instaneous voltage of the carrier signal at the base of Q3 is less than the instantaneous voltage of the modulation signal at the base of Q2, transistors Q1, Q2 act as emitter followers, transistor Q3 is cut-off, and the output signal at 17 follows the voltage at the base of Q2. When the instantaneous carrier voltage lies between the instantaneous voltages at the bases of Q1, Q2, Q1, Q3 act as emitter followers, Q2 is cutoff, and the output follows the voltage at the base of Q3. When the instanteous carrier voltage exceeds the instantaneous voltage at the base of Q1, Q1 cuts-off, and any further rise in output voltage is limited by the high source impedance of the carrier signal generator. Thus the output signal is a form of the carrier with its peaks clipped at the instantaneous levels of the modulation inputs at the bases of Q1, Q2, Figs. 2(a), 2(b), 2(c) (not shown). Two such modulators may be fed with antiphase inputs to give a suppressed carrier output. The modulation amplifier comprises a drift connected amplifier Q8, Q9, Q10 feeding to stages Q6, Q7 which produce the antiphase output signal superimposed on appropriate D.C. leads. The power supply to the circuit (not shown) comprises a series transistor with its base connected to two further transistor strapped as diodes. Q6, Q7 may be replaced by a single transistor with one output taken from the emitter circuit and one from the collector.