Design and performance of precision miniature TCXOs
Ever since the advent of quartz crystals as frequency control devices, there has been an ongoing quest to improve their temperature stability. After a brief review of the history of crystal oscillator temperature compensation, this article will describe the current state-of-the-art in TCXO temperature-compensation technology and the associated crystal resonators.
When the first crystal oscillators were built in the 1920s, the only crystals available, such as the X-cut, exhibited poor temperature performance. The development of the AT-cut crystal was a major step toward making temperature compensation feasible
Thermistor/resistor network compensation
Thermistor/resistor TCXOs have been the mainstay of crystal oscillator temperature compensation for 50 years. A correction voltage generated by a network of one or more thermistors cancels the frequency vs. temperature variation of a voltage-controlled crystal oscillator. The introduction of voltage-variable capacitance varactor diodes along with improvements in negative-temperature coefficient thermistors made it possible to compensate crystals to a greater precision
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