Phase-locked loop and compound MOS capacitor thereof
AssigneeVIA Technologies, Inc.
InventorHsiao-Chyi Lin
Life of this patent
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Abstract
Compound MOS capacitors and phase-locked loop with the compound MOS capacitors are disclosed. In the phase-locked loop, the compound MOS capacitors of the loop filter are HV (high voltage) devices, and the voltage control oscillator is a LV (low voltage) device. The compound MOS capacitor comprises a HV PMOS capacitor having a base coupled to a source terminal of a low voltage source and a HV NMOS capacitor having a base coupled to a ground terminal of the low voltage source. The gates of the HV PMOS capacitor and the HV NMOS capacitor are connected together to receive a control voltage. The capacitance of the compound MOS capacitor is near constant in any control voltage.
Claims10
A compound MOS capacitor, comprising:
- a HV PMOS capacitor with a HV PMOS threshold voltage, having a base coupling to a source terminal of a low bias voltage source;
- and
- a HV NMOS capacitor with a HV NMOS threshold voltage, having a base coupling to a ground terminal of the low bias voltage source,
- wherein a gate of the HV PMOS capacitor is connected with a gate of the HV NMOS capacitor to receive a control voltage,
- wherein a voltage difference between a voltage value of the source terminal of the low bias voltage source and an absolute value of the HV PMOS threshold voltage approximates to the HV NMOS threshold voltage.
A phase-locked loop, comprising:
- a phase frequency detector, measuring phase difference and frequency difference between a reference signal and a feedback signal;
- a charge pump, comprising a charge circuit and a discharge circuit, and switching between the charge circuit and the discharge circuit according to the phase difference and the frequency difference of the reference signal and the feedback signal;
- a loop filter, comprising at least one compound MOS capacitor charged/discharged by the charge pump to adjust the voltage level of an output terminal of the loop filter;
- and
- a voltage control oscillator, outputting an oscillating signal, and adjusting the frequency of the oscillating signal according to the voltage level of the output terminal of the loop filter;
- wherein the compound MOS capacitor comprises:
- a HV PMOS capacitor with a HV PMOS threshold voltage, having a base coupled to a source terminal of a low bias voltage source;
- and
- a HV NMOS capacitor with a HV NMOS threshold voltage, having a base coupled to a ground terminal of the low bias voltage source;
- wherein a gate of the HV PMOS capacitor is connected with a gate of the HV NMOS capacitor and work as a control terminal of the compound MOS capacitor,
- wherein a voltage difference between a voltage value of the source terminal of the low bias voltage source and an absolute value of the HV PMOS threshold voltage approximates to the HV NMOS threshold voltage.
Dependencies are inferred from the claim text.