Dual-loop phase-locked loop
AssigneeLSI Logic Corporation
InventorsAlan S. Fiedler, Daniel J. Baxter
Life of this patent
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Abstract
An integrated circuit phase-locked loop includes a phase/frequency detector, a charge pump, and a voltage-controlled oscillator (VCO) which are coupled together in series. The VCO has first and second VCO control inputs, and has a VCO output which is coupled to the phase/frequency detector. An off-chip loop filter input is coupled between the charge pump and the first VCO control input for coupling to an off-chip loop filter. An on-chip loop filter is coupled between the first VCO control input and the second VCO control input. The VCO has a lower voltage-to-frequency gain from the first VCO control input to the VCO output than from the second VCO control input to the VCO output.
Claims12
An integrated circuit comprising:
- a phase/frequency detector, a charge pump, and a voltage-controlled oscillator (VCO) which are coupled together in series to form a phase-locked loop, wherein the VCO has first and second VCO control inputs and has a VCO output coupled to the phase/frequency detector, and wherein the VCO has a lower voltage-to-frequency gain from the first VCO control input to the VCO output than from the second VCO control input to the VCO output;
- an off-chip loop filter input coupled between the charge pump and the first VCO control input;
- and
- an on-chip loop filter coupled between the first VCO control input and the second VCO control input.
A phase-locked loop comprising:
- an integrated circuit comprising:
- a phase/frequency detector, a charge pump, and a voltage-controlled oscillator (VCO) which are coupled together in series, wherein the VCO has first and second VCO control inputs coupled to the charge pump and has a VCO output, and wherein the VCO has a lower voltage-to-frequency gain from the first VCO control input to the VCO output than from the second VCO control input to the VCO output;
- and
- an on-chip loop filter coupled between the first VCO control input and the second VCO control input;
- and
- an off-chip loop filter coupled between the charge pump and the first VCO control input, wherein the off-chip loop filter is located off of the integrated circuit.
A method of generating a feedback signal in a phase-locked loop (PLL) on an integrated circuit, the method comprising:
- comparing a phase and frequency of a reference signal to a phase and frequency of the feedback signal and generating a charge pump control signal as a function of the comparison;
- pumping charge onto and off of a circuit node as a function of the charge pump control signal;
- generating first and second frequency control voltages based on the charge pumped onto and off of the circuit node;
- filtering the first frequency control voltage with an off-chip loop filter;
- filtering the second frequency control voltage with an on-chip loop filter;
- controlling the phase and frequency of the feedback signal as a function of the filtered first frequency control voltage;
- and
- controlling a center frequency of the feedback signal and as a function of the filtered second frequency control voltage.
Dependencies are inferred from the claim text.