Calibration circuit for VCO
AssigneeBroadcom Corporation
InventorSeema Butala Anand
Life of this patent
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Abstract
A phase-locked loop circuit includes an array of selectable capacitors formed within the phase-locked loop circuit to enable the phase-locked loop circuit to provide a degree of coarse frequency control by adding or removing capacitors and a degree of fine frequency control by sinking or sourcing current from a charge pump into a loop filter. A finite state machine is provided within a voltage controlled oscillator calibration circuit that communicates with an external baseband processor to initiate a calibration process, and further to determine how many capacitors of an array of capacitors if formed within the phase-locked loop circuit should be coupled to provide the coarse frequency control.
Claims21
A phase-locked loop system formed within a radio receiver, comprising:
- a phase-locked loop circuit for providing a signal having a specified frequency characteristic;
- a voltage controlled oscillator calibration circuitry for providing a calibration output signal to the phase-locked loop circuit that specifies how many selectable capacitors of a plurality of capacitors formed within the phase-locked loop circuit are to be selectively coupled to a node within the phase-locked loop circuit while the phase-locked loop system is operating in a calibration mode;
- wherein the voltage controlled oscillator calibration circuitry further includes a finite state machine is coupled to receive a first control signal and is formed to initiate a calibration process whenever the first control signal is received;
- and wherein the voltage controlled oscillator calibration circuitry further includes a plurality of comparators, the plurality of comparators being coupled to receive a VCO voltage and each coupled to receive one of a plurality of threshold voltages for comparing to the VCO voltage.
A phase-locked loop circuit, comprising:
- a phase frequency detector for detecting a phase difference between a reference input signal and a feedback signal for producing a voltage that represents the detected phase difference;
- a charge pump coupled to receive the voltage representing the detected phase difference, the charge pump for generating a DC current level responsive to the received voltage:
- a loop filter coupled to receive the DC current generated by the charge pump, the loop filter for converting the received current into a voltage level;
- a voltage controlled oscillator coupled to receive the voltage level, the voltage controlled oscillator for producing an output signal having a frequency characteristic which frequency characteristic is a function of the received voltage level;
- and an array of selectable capacitors formed within the phase-locked loop circuit, the selectable capacitors for adjusting the frequency characteristic of the output signal from the phase-locked loop circuit.
A method for controlling a frequency of an output signal of a phase-locked loop circuit, comprising:
- setting a capacitance value by selecting a first number of capacitors formed within the phase-locked loop circuit to provide a level of coarse frequency-control;
- sinking current out of a loop filter formed within the phase-locked loop circuit to provide fine frequency control whenever an input voltage to a voltage controlled oscillator is higher than a specified amount;
- sourcing current into the loop filter for fine frequency control whenever the input voltage to a voltage controlled oscillator is lower than a specified amount;
- evaluating a voltage at a node within the loop filter to determine whether the voltage within a specified threshold range;
- and generating a ready control signal if the voltage is within the specified threshold range generating an error signal if the voltage is not within the specified threshold range and no capacitors may be coupled or decoupled to and from the phase-locked loop circuit..
Dependencies are inferred from the claim text.