PLL circuit including a voltage controlled oscillator and a method for controlling a voltage controlled oscillator
View Patent ↗A voltage controlled oscillator having a wide oscillation frequency band, desirable carrier-noise characteristic, and desirable linearity of the oscillation frequency relative to a control voltage. The voltage controlled oscillator includes an oscillation unit and a control unit. The oscillation unit generates an output signal having an oscillation frequency corresponding to the control voltage in one of a plurality of oscillation frequency bands. The oscillation unit includes a switching unit for selecting one of the plurality of oscillation frequency bands in accordance with a switching signal. The control unit generates the switching signal in accordance with the control voltage.
1. A voltage controlled oscillator comprising:
an oscillation unit which generates an output signal having an oscillation frequency corresponding to a control voltage in one of a plurality of oscillation frequency bands, wherein the oscillation unit includes:
a fixed inductor;
a variable capacitor connected to the fixed inductor and having a capacitance varied in accordance with the control voltage; and
a fixed capacitor connected in parallel with the variable capacitor;
a plurality of additional inductors;
a plurality of switch circuits connected to the additional inductors to selectively connect the additional inductors in parallel with the fixed inductor in accordance with a switching signal; and
a control unit connected to the switch circuits which generates the switching signal in accordance with the control voltage.
2. The voltage controlled oscillator according to claim 1 , wherein the control unit includes a plurality of comparators having different threshold values.
3. The voltage controlled oscillator according to claim 2 , wherein each of the comparators has a hysteresis characteristic, in which a rising threshold value is greater than a trailing threshold value.
4. A method for controlling a voltage controlled oscillator, wherein the voltage controlled oscillator includes a fixed inductor and a plurality of additional inductors, the method comprising:
generating an output signal having an oscillation frequency corresponding to a control voltage in one of a plurality of oscillation frequency bands;
generating a switching signal in accordance with the control voltage; and
selectively connecting the additional inductors in parallel with the fixed inductor in accordance with the switching signal.
5. The method according to claim 4 , wherein the voltage controlled oscillator includes a variable capacitor connected to the fixed inductor and has a capacitance varied in accordance with the control voltage, and a fixed capacitor connected to the variable capacitor, the method further comprising:
setting the oscillation frequency band in accordance with the fixed inductor, the variable capacitor, the fixed capacitor, and at least one of the additional inductors.
6. A PLL circuit comprising:
a voltage controlled oscillator including:
an oscillation unit which generates an output signal having an oscillation frequency corresponding to a control voltage in one of a plurality of oscillation frequency bands, wherein the oscillation unit includes:
a fixed inductor;
a variable capacitor connected to the fixed inductor and having a capacitance varied in accordance with the control voltage; and
a fixed capacitor connected in parallel with the variable capacitor;
a plurality of additional inductors;
a plurality of switch circuits connected to the additional inductors to selectively connect the additional inductors in parallel with the fixed inductor in accordance with a switching signal; and
a control unit connected to the switching unit which generates the switching signal in accordance with the control voltage.