Integrator controlled time compensated clock oscillator

Abstract

A time compensated clock oscillator (TCCO) is provided with an integrator to produce stability of the output frequency. The integrator is connected between the D/A converter and the voltage controlled crystal oscillator (VCXO) of the TCCO. The output frequency of the VCXO is fed back to a frequency counter, which samples the output, determines its average frequency, and compares it with a reference frequency. A microprocessor corrects the reference frequency for temperature changes, determines the output frequency error, calculates the output frequency drift rate, and provides a digital correction signal. The D/A converter converts the digital correction signal to an input voltage for the integrator. The integrator produces a ramp-shaped control voltage for input to the VCXO. Because the control voltage produced by the integrator changes smoothly over the interval between samples by the frequency counter, the output frequency drift rate of the VCXO is continuously corrected to produce improved short-term frequency stability.

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