VCO circuit and PLL circuit thereof

摘要

A VCO circuit has a voltage variable capacitance device CVD2 connected in series with or in parallel to a capacitor C3 connected in series with an inductance L1, which constitutes a resonator of the VCO circuit. An adiustment voltage VD2 is applied to a cathode of the voltage variable capacitance device CVD2, such that the relation between a control voltage VD1 and an oscillation frequency fo of the VCO circuit is electrically adjusted to enable improvement of the fabrication yield. The control voltage VD2 may be derived from control date from 1 via a D/A converter 2 or a control voltage applied to one end of coil LB. Device CVD2 may be included in the emitter circuit instead of the base circuit. The VCO may form part of a phase locked loop and the control voltage applied to the VCO is also applied via a further control loop including A/D, D/A converters, controller, CVD2 of the PLL VCO (figs. 10 not shown).