VCO having adjustment for fluctuations in relation between control voltage and output frequency

A VCO circuit, comprising:

• a) a first voltage variable capacitance device for varying a resonance frequency of a resonance circuit comprising a fixed capacitance device connected in series with an inductance device,
• b) a second voltage variable capacitance device connected to said fixed capacitance device, and
• c) means for applying an adjustment voltage to said second voltage variable capacitance device to adjust for fluctuations in the relation between a control voltage applied to the first voltage variable capacitance device and a resonance frequency of said resonance circuit;
• wherein said fixed capacitance device comprises a series circuit of first, second, and third capacitors, and said second voltage variable capacitance device is connected in parallel to one of the first, second, and third capacitors.

A PLL circuit employing a VCO circuit, comprising:

• a) a VCO circuit [(13)] having a first voltage variable capacitance device for varying a resonance frequency of a resonance circuit comprising a fixed capacitance device connected in series with an inductance device, a second voltage variable capacitance device connected to said fixed capacitance device, and means for applying an adjustment voltage to said second voltage variable capacitance device to adjust for fluctuations in the relation between a control voltage applied to the first voltage variable capacitance device and a resonance frequency of said resonance circuit,
• b) a reference frequency oscillator [(10)] for oscillating a reference frequency;
• c) a fixed-frequency divider [(11)] for dividing the reference frequency;
• d) a variable frequency divider [(14)] for dividing an oscillation frequency of the VCO circuit;
• e) a phase comparator [(12)] for comparing the phase of the frequency divided by said variable frequency divider with the phase of the frequency divided by said fixed-frequency divider;
• f) a filter [(15)] for applying a control voltage based on a smoothed output of said phase comparator to the first voltage variable capacitance device of the VCO circuit;
• and
• g) an adjusting circuit [(18,19,20)] for comparing the oscillation frequency of the VCO circuit, corresponding to an external controller [(17)] command, with the control voltage output by said filter, and outputting the adjustment voltage to be applied to said second voltage variable capacitance device of the VCO circuit to cause the control voltage output by said filter to be in a predetermined voltage range when the VCO oscillates at a predetermined frequency.