GB893810A - Improvements relating to oscillators incorporating transistors - Google Patents

Abstract

893,810. Frequency modulation; frequency shift signalling; transistor oscillator circuits. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Feb. 2, 1961 [Feb. 17, 1960], No. 5649/60. Classes 40(5) and 40(6). A transistor phase shift oscillator comprises two transistors T1, T2 with opposite phase shift networks N1, N2 connected between collector and emitter of each and the output of each network connected to the base of the other transistor. Further, a modulation path including a transformer TR is connected between the emitter circuits, and the transformer secondary may be connected to a symmetrical transistor T3 so that depending on whether T3 is fully conductive or not the modulation path is effective or not to shift the oscillator frequency in accordance with D.C. telegraph signals of opposite polarity appplied to T3, the latter otherwise being only partially conductive due to the oscillator frequency. The main feedback, due to the D.C. path through resistor R14, is such that D.C. stabilization of the working point of the transistors is obtained by negative feedback and the capacitor by-passed resistors R1, R4, R8, R9, R12 serve to increase the D.C. gain. Load resistors R2, R3, R10, R11 may be about equal. In a modification inductors are included in series with resistors R5, R14 and resistors in series with capacitors C3, C7. The oscillator may be of voice frequency.