Abstract
This paper describes a VCO (Voltage Controlled Oscillator) by ceramic resonator with variable reactance circuit using positive/negative capacitance circuit. Because ceramic resonator is made of stable piezoelectric ceramics and its oscillation frequency is primarily adjusted by the size and thickness of the ceramic element, a ceramic resonator has high oscillation and Q stabilities. Ceramic resonator is frequently used as VCO by adding external variable capacitance circuit. But external capacitance gives a negative effect that an oscillation frequency should go down lower than physical fixed value. The variable reactance circuit realized by positive and negative capacitance circuit can make the oscillation frequency either decrease or increase. Additionally, when a reactance circuit is balanced on neither positive nor negative, the ceramic resonator's oscillation frequency is equal to physical fixed value unaffected by reactance circuit. We designed the oscillation circuit and variable reactance circuit suitable for LSI, and we built this VCO with reactance circuit onto PLL system for evaluation.
