GB789428A - Transistor frequency converter - Google Patents

Abstract

789,428. Transistor frequency converting circuits. HAZELTINE CORPORATION. April 12, 1956 [May 5, 1955], No. 11179/56. Class 40 (6). In a circuit in which a signal input 21 is applied to a transistor 22 associated with a regenerative oscillatory system 50 coupled to the input to produce a beat frequency signal in circuit 12, and in which the regenerative system includes the internal base impedance tending to prevent oscillation, a reactance 42 is provided to compensate the phase shift in the feed-back path thereby maintaining oscillation. The circuit is described as applied to a radio receiver in which an aerial 17 is coupled to a tuned circuit 18, 20 and a coupling coil 21 applies a radio frequency signal between the base 31 and emitter 35 of the transistor, capacitor 42 acting as a by-pass. An inductor 43 in the collector circuit is coupled to tuned circuit 39, 40 which determines the frequency of the local oscillation, a tap on coil 39 being connected to the emitter. The collector current passes to a tap on the inductor of circuit 12 tuned to the intermediate frequency, the output passing through amplifier 13 to detector. 14 and thence to the amplifier 15 and speaker 16 The transistor is of a type in which the internal base resistance is large compared with the base impedance. In the equivalent diagram, Fig. 3, it is assumed that the internal emitter resistance can be neglected and the impedance is in the form of a capacitor Cb<SP>1</SP>e and the emitter resistance is rbb<SP>1</SP>. With capacitor 42 operating as a short-circuit, switch S closed, the feed-back potential E<SP>1</SP> feeds a current I<SP>1</SP> through the base circuit to generate a voltage Eble in the effective input to the transistor. This voltage produces an in-phase collector current ic and voltage Ec, a fraction of which appears across the tap on inductor 39. The variation in phase with frequency is such that when the phase of the feed-back is correct the gain of the circuit may be insufficient. By introducing a further reactance 42 the current I<SP>1</SP> is caused to lead so that the resulting feed-back voltage is more nearly in phase with the input E<SP>1</SP> and the circuit oscillates more nearly to the resonant frequency of circuit 39, 40 and the gain is maintained. Vector diagrams, Figs. 4 and 5 (not shown), illustrate the effect of employing capacitor 42.