Temperature compensated crystal oscillator

摘要

A temperature compensated crystal oscillator having a crystal resonator uses a single thermistor and no expensive varactor. The compensation circuit includes, a low temperature compensation circuit consisting of a first fixed capacitor and a first diode in series, a high temperature compensation circuit consisting of a second fixed capacitor and a second diode in series, and an intermediate temperature compensating circuit consisting of a third capacitor having a negative temperature coefficient. All three circuits are in parallel with each other and in series with the crystal resonator of the oscillator. A thermistor is connected to the anodes of both diodes and biasing resistors and connected to the cathode of the second diode whereby a temperature dependent forward bias is applied to the first diode at all temperatures and to the second diode only at the high temperatures.