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We present a new temperature compensation system for microresonator-based frequency references. It consists of a phase-locked loop (PLL) whose inputs are derived from two microresonators with different temperature coefficients of frequency. The resonators are suspended within an encapsulated cavity and are heated to a constant temperature by the PLL controller, thereby achieving active temperature compensation. We show repeated real-time measurements of three 1.2-MHz prototypes that achieve a frequency stability of ?? 1 ppm from -20??C to +80??C, as well as a technique to reduce steady-state frequency errors to ??0.05 ppm using multipoint calibration.
Date of Publication: Feb. 2010