GB811095A - Stabilised electric transistor oscillators - Google Patents

Abstract

811,095. Transistor oscillators. STANDARD TELEPHONES & CABLES Ltd. Oct. 18, 1957, No. 32583/57. Class 40 (6). In a, transistor oscillator, amplitude stabilization is effected by means of a " directlyheated " thermistor 16 arranged effectively in parallel with the output of the oscillator and a " block " thermistor 19 arranged in series with a feedback path interconnecting the collector and emitter circuits of the transistor. In the circuit shown comprising a parallel-tuned circuit 10, 12 forming part of the load in the collector circuit of the transistor and a piezoelectric crystal 21 connected in series in the feedback path, the crystal and tuned circuit being resonant at the same frequency, the " directly-heated " thermistor 16, whose resistance depends on the current flowing through it as well as on the ambient temperature, operates to maintain the output of the oscillator constant for a constant ambient temperature. However, the thermistor will not be able to correct for output variations caused by a change in ambient temperature: to correct for these the " block " thermistor 19, whose resistance is substantially independent of current flow through it, is provided so that when, for example, the temperature rises and thermistor 16 tends to stabilize the output at a lower level, the resistance of thermistor 19 falls to increase the positive feedback and hence the output level. A resistance 23 is arranged in parallel with thermistor 19 to match its temperature characteristics with those of thermistor 16. The Specification states that the piezo-electric crystal 21 may be replaced by a conventional series-resonant circuit or by a resistor in which case the circuit 10, 12 would be the sole frequency-determining circuit.