GB1000483A - Improvements in transistor oscillator and amplifier circuits - Google Patents

Abstract

1,000,483. Transistor amplifying and oscillating circuits. M.S.S. RECORDING CO. Ltd. Dec. 27, 1961 [Dec. 28, 1960], No. 44451/60. Heading H3T. In a transistor amplifying or oscillating circuit at least one transistor is caused to operate in its saturation state for a major part of the period when it is conducting by connecting two inductors to the transistor, one of the inductors being in parallel with a capacitor, such that for alternating current purposes the transistor acts as a short circuit connecting the two inductors in parallel with each other. In an oscillator circuit, Fig. 1, a transistor T has two inductors L1, L2 connected as shown with capacitor C3 connected between collector and earth, feedback being provided by phase shifting network L3 and C2. When the transistor conducts it acts as a switch to connect for A.C. purposes the inductor L2 in parallel with the parallel combination of inductor L1 and capacitor C3, the impedance of the D.C. source being negligible. Thus the difference in potential between the collector and emitter electrodes of the transistor will remain small and the transistor will operate in its saturation state, for any variations in the oscillatory voltage produced by the circuit are closely followed by the emitter and collector together. In a further embodiment, Fig. 2 (not shown) the earth and negative supply terminals are reversed and the emitter of the transistor is connected to the positive supply line which is no longer at earth potential. In Fig. 3 (not shown) the collector of the transistor is directly connected to the negative supply line and the two inductors are connected between the emitter and positive supply line, the junction points of the two inductors being earthed. Fig. 4 shows a push-pull oscillator comprising two transistors T1, T2 operated in their saturated state, the circuit including a centretapped collector inductor L1 tuned by capacitor C1 and a centre-tapped emitter inductor L4. During each half cycle of operation the transistor which is conducting connects two inductors in parallel as described in the first embodiment so that the difference in potential of the emitter and collector electrodes remains small. Diodes MR1 and MR2 provide temperature compensation to the circuit. In the circuits of Fig. 5 and Figs. 6, 7 (not shown) a tuned amplifier includes inductors L1, L2 which for A.C. purposes are connected in parallel with each other by transistor T when the latter conducts, so that the collector and emitter follows together the variations in output voltage and allow the transistor to operate in its saturation state.