GB1160603A - Improvements in or relating to Transistorised Modulatable Oscillation Generators, Demodulators, Phase Detectors and Frequency Shifters - Google Patents

Abstract

1,160,603. Transistor circuits. MARCONI CO. Ltd. 5 April, 1968 [19 July, 1967], No. 33137/67. Headings H3A, H3R and H3T. An amplitude modulator, demodulator, phase detector, or frequency changer comprises: first and second pairs of emitter coupled transistors T1, T2 and T3, T4, having an output load R1 common to T2, T3; a frequency determining circuit, e.g. crystal K, coupling the collector circuit of T4 to the base circuit of T1 and also to T3; means T5, T6 for applying antiphase signals to the common emitter circuits of the two pairs; and means for maintaining the bases of T2, T4 at a fixed potential. The arrangement is such that the two pairs act as alternately closing switches which close, one on the positive and one on the negative half-cycles, of a signal of frequency determined by the crystal K. An additional transistor T9 may be included to eliminate capacitive coupling to the output from the base of transistor T3. If the signal at IN is a modulation signal, or a signal to be frequency shifted, the resulting output is a suppressed carrier signal, from which one sideband may be removed by filtering. If the input is a suppressed carrier signal, and the frequency generated by crystal K is at the desired carrier frequency, the output is the modulation. If the input is a signal at the generated frequency, the circuit functions as a phase comparator. A capacitor may be added between the junction of D2, R6 and the emitter of T8 if a balanced supply is not provided, Fig. 4 (not shown).