Oscillator with logic inverter gates - uses varactor diodes for frequency range of several KHz to several MHz

摘要

A series of three logic inverter gates are fed from an emitter follower, of npn type and DC negative feedback to the transistor base is obtained from the series gate chain via the centre tapped coil of the resonant cct formed with two varactor diodes. AC feedback is via a capacitor from the penultimate series gate giving, with the feedback resistance, correct phasing for oscillation. Input to the transistor is via a parallel resistor and capacitance output is taken from three parallel gates giving inverted or non-inverter outputs.