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Abstract

A multimode oscillator is disclosed which employs a single gain feedback loop for exciting at least two modes of a resonator to cause the oscillator to oscillate simultaneously at at least two frequencies. The multi-mode oscillator comprises the resonator, an amplifier to provide gain at the appropriate operating frequencies to support simultaneous oscillation at such frequencies and an equalizing network with amplitude and phase characteristics versus frequency to support the simultaneous modes of oscillation. The single loop oscillator permits separate control of the two simultaneous different frequencies of oscillation. In order to minimize thermal hysteresis, at least the active portion of the feedback loop does not include inductors. In some applications, the multimode oscillator may include one or more rejection networks to suppress unwanted oscillations. The useful outputs of the multimode oscillator are one or more of the operating frequencies, harmonics and intermodulation products. In one specific embodiment, one output is at the frequency of the fundamental C-mode resonance of an SC-cut lateral field quartz crystal, and a second output is at the beat frequency between the third harmonic of that fundamental and the third overtone. The beat frequency is a measurement of effects, such as temperature, upon the frequencies of operation of the oscillator.

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First Claim