Method and Apparatus to Improve Performance of GPSDO's and other Oscillators

A method of calibrating a frequency of a crystal oscillator comprising:

• measuring a first Electronic Frequency Control (EFC) voltage established by locking said crystal oscillator to a frequency reference signal and the first EFC voltage obtaining a steady state value;
• storing data corresponding to the first EFC voltage in a memory;
• locking said crystal oscillator to the reference signal in response to a first power-on event;
• measuring a second EFC voltage established by the reference signal and the first power-on event;
• establishing a prediction of a change of frequency during the first hours of operation based on the first and second EFC voltages;
• and
• generating an error-correction voltage during at least a portion of the first hours of operation, thereby reducing the frequency errors caused by crystal retrace,
• wherein the generating occurs in response to a second power-on event occurring in conjunction with the absence of said frequency reference signal and wherein the error-correction voltage is based on said prediction.

An electronic circuit comprising:

• a controller coupled to a crystal oscillator in a control loop, said control loop establishing an operating baseline for said crystal oscillator using a frequency reference,
• wherein said controller includes a memory to store information corresponding to said operating baseline,
• wherein said controller adjusts a frequency according to said information, thereby correcting said frequency of said crystal oscillator, and
• wherein said adjusting occurs in response to a power-on event and the absence of said frequency reference.