'Single-pin' integrated crystal oscillators

Oscillator configurations for integrated circuit (IC) applications where the quartz resonator can be connected between one pin of the IC and ground are presented. Excellent performance and good designability are obtained by applying negative feedback around a high-gain amplifier circuit and by including a symmetrical limiter in the feedback loop. The feedback mechanism provides an inherent buffering against load variations. Implementation examples in bipolar technology are discussed. A simple model for the negative impedance at the crystal port reveals methods for avoiding parasitic oscillations due to the shunt capacitance of the crystal. The performance of a semicustom integrated oscillator with simple structure is simulated and measured. In this oscillator, a novel start-up technique that ensures a stable and reliable start-up behavior is used.<
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