Self-calibrating phase locked loop charge pump system and method
AssigneeAnalog Devices, Inc.
InventorChristophe C. Beghein
Life of this patent
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Abstract
A charge pump circuit is disclosed that includes a positive current output circuit for providing a positive current to an output of the charge pump circuit, a negative current output circuit for providing a negative current to the output of the charge pump circuit, and a calibration unit for permitting the charge pump circuit to be adjusted to reduce any current mismatch between the positive and negative currents and to provide that any current mismatch is integrated into a PLL loop filter capacitance.
Claims20
A charge pump circuit comprising:
- a positive current output circuit for providing a positive current to an output of the charge pump circuit;
- a negative current output circuit for providing a negative current to the output of the charge pump circuit;
- and
- calibration means for permitting the charge pump circuit to be adjusted to reduce any current mismatch between the positive and negative currents and for providing that any current mismatch is integrated into a phase locked loop filter capacitance.
A charge pump circuit comprising:
- a reference current circuit operable for defining a reference current through a first biasing transistor and having a first low output impedance associated therewith, said reference current circuit being coupled to a first output transistor to provide a negative current to an output of the charge pump circuit;
- a replication feedback circuit coupled to said reference current circuit at a coupling node and operable for replicating said output voltage at said coupling node such that said reference current is defined in a second biasing transistor and having a second low impedance, said replication feedback circuit being coupled to a second output transistor to provide a positive current to the output of the charge pump circuit;
- and
- calibration means for permitting the charge pump circuit to be adjusted to reduce any mismatch between the positive and negative currents.
A charge pump circuit comprising:
- a reference current circuit including a first operational amplifier having a positive input port and a negative input port, said reference current circuit being operable for defining a reference current through a first biasing transistor and having a first low output impedance associated therewith, and being coupled to a first output transistor to provide a negative current to an output of the charge pump circuit;
- a replication feedback circuit including a second operational amplifier having a positive input port and a negative input port, said replication feedback circuit being coupled to said reference current circuit at a coupling node and operable for replicating said output voltage at said coupling node such that said reference current is defined in a second biasing transistor and having a second low impedance, and being coupled to a second output transistor to provide a positive current to the output of the charge pump circuit;
- and
- reconfiguration means for permitting the charge pump circuit to be reconfigured to couple the positive input ports of the first and second operational amplifiers to the output voltage of the charge pump circuit and to couple the negative input ports of the first and second operational amplifiers to a reference voltage.
A method of calibrating a charge pump circuit in a phase locked loop, said method comprising the steps of:
- causing a voltage on a PLL loop filter capacitor to be equal to a reference voltage;
- integrating a current difference into a phase locked loop filter capacitance;
- and
- comparing the PLL loop filter voltage to a reference voltage.
Dependencies are inferred from the claim text.