Phase-locked loop bandwidth calibration circuit and method thereof
AssigneeAnalog Devices, Inc.
InventorsEdmund J. Balboni, Wyn T. Palmer, Jonathan R. Strange
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Abstract
A phase-locked loop frequency synthesizer has a charge pump, phase-locked loop filter, voltage-controlled oscillator, and a bandwidth calibration circuit. The bandwidth calibration circuit measures the gain of the voltage-controlled oscillator and uses the measured voltage-controlled oscillator gain to adjust the charge pump level. The charge pump level is adjusted so that a product of the voltage-controlled oscillator gain and the measured charge pump level results in a constant phase-locked loop bandwidth.
Claims15
A phase-locked loop bandwidth calibration circuit, comprising:
- a programmable charge pump;
- a phase-locked loop filter operatively connected to said programmable charge pump;
- an oscillator, operatively connected to said phase-locked loop filter, to generate a frequency signal based upon a signal received from said phase-locked loop filter;
- and
- a control loop operatively connected to said phase-locked loop filter and said programmable charge pump;
- said control loop including a gain measurement circuit, operatively connected to said oscillator, to measure a gain of said oscillator;
- said control loop controlling said programmable charge pump to adjust its output current level based on the measured gain of said oscillator;
- said gain measurement circuit including,
- a voltage difference measurement circuit, operatively connected to said phase-locked loop filter, to measure a voltage difference corresponding to two voltages being output from said phase-locked loop filter at different times,
- an analog to digital converter, operatively connected to said voltage difference measurement circuit, to convert the measured voltage difference into a digital signal, and
- a controller to cause said programmable charge pump to adjust its output current level based upon a received digital signal from said analog to digital converter.
A phase-locked loop bandwidth calibration circuit, comprising:
- a programmable charge pump;
- a phase-locked loop filter operatively connected to said programmable charge pump;
- an oscillator, operatively connected to said phase-locked loop filter, to generate a frequency signal based upon a signal received from said phase-locked loop filter;
- a control loop operatively connected to said phase-locked loop filter and said programmable charge pump;
- said control loop including a gain measurement circuit, operatively connected to said oscillator, to measure a gain of said oscillator;
- said control loop controlling said programmable charge pump to adjust its output current level based on the measured gain of said oscillator;
- a programmable gain amplifier;
- a comparator for comparing a voltage of an output from said programmable gain amplifier with a voltage necessary to produce a predetermined frequency shift in said oscillator to produce a gain signal;
- and
- a gain controller, in response to said gain signal produced by said comparator, to control a gain of said programmable gain amplifier.
A method of calibrating a phase-locked loop bandwidth, comprising:
- (a) setting a phase-locked loop at a local oscillator offset;
- (b) allowing the phase-locked loop to settle;
- (c) measuring, after allowing the phase-locked loop set to the local oscillator offset to settle, a first voltage of a voltage-controlled oscillator located in the phase-locked loop;
- (d) setting the phase-locked loop to a channel center frequency;
- (e) allowing the phase-locked loop to settle;
- (f) measuring, after allowing the phase-locked loop set to the channel center frequency to settle, a second voltage of the voltage-controlled oscillator;
- (g) determining a difference between the first and second voltage measurements;
- and
- (h) controlling a programmable charge circuit located in the phase-locked loop to adjust its output current level based on the determined voltage difference.
Dependencies are inferred from the claim text.