GB1389203A - Transistorised oscillators - Google Patents

Abstract

1389203 Transistor crystal oscillators BRITISH OXYGEN CO Ltd [trading as EDWARDS HIGH VACUUM INTERNATIONAL] 5 June 1972 [5 May 1971] 13372/71 Heading H3T [Also in Division G3] In an oscillator circuit including a piezoelectric crystal X connected for series resonance between the emitter of a first transistor T1 and earth, the connection between the crystal and earth is direct without interposition of any component and a second transistor T2 has its base coupled to the collector of the first transistor, its emitter arranged to be maintained in operation at a fixed potential and its collector connected to its base through a resistor R3 to provide negative feedback and coupled to the base of the first transistor T1. The oscillator output voltage Vo is maintained constant by the operation of transistors T3 and T4 which operate to limit the voltage across the crystal X. To avoid distortion due to overloading of the transistor T1 when the resistance of the crystal X is small, the value of R3 is increased and an additional resistor R12 is inserted to reduce the alternating voltage at the base of T1. A capacitor C5 provides a phase shift to compensate for the effect of cable capacitance in parallel with the crystal X. A simplified version of the oscillator including only R1-R4, C, X and T1, T2 is described (Fig. 1, not shown) and circuits in which T1 and T2 are both of PNP type or T1 is NPN type and T2 is PNP type are described (Figs. 2 and 3, not shown).