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US 5,687,201 AGranted
Phase-locked-loop with linear combination of charge pump and current controlled oscillator
AssigneeStandard Microsystems Corporation
InventorsKelly Patrick McClellan, Parameswaran K. Gopalier, Khosrow Haj Sadeghi
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Abstract
A phase-locked-loop (PLL) has a current controlled oscillator (ICO) whose gain varies with its input current. The PLL also contains a charge pump that controls the input current of the ICO and therefore the output frequency of the ICO. The charge pump has a gain that is controlled by the ICO input current in a manner which linearizes the combination of charge pump and ICO. This results in a substantially constant loop gain for a PLL.
Claims12
A phase-locked-loop comprising:
- a phase comparator for receiving first and second periodic signals, and for providing a frequency up signal if the second signal lags the first signal and a frequency down signal if the second signal leads the first signal;
- a charge pump for generating positive current levels in response to the frequency up signal and negative current levels in response to the frequency down signal, the magnitude of the positive and negative current levels being variable and being dependent on a charge pump current;
- an accumulator for accumulating charges of said positive and negative current levels and for generating a voltage in response to the accumulated charge;
- a voltage-to-current converter for converting said voltage of said accumulator into a control current;
- and
- a current controlled oscillator for generating said second signal in response to said control current, the frequency of said second signal being dependent on said control current;
- said charge pump current also being dependent on said control current,
- wherein said charge pump current has a minimum value B, said value B insures that said charge pump current has a non-zero value, and said control current has to be above a threshold A to cause an increase in said charge pump current.
5 more elements
A phase-locked-loop, comprising:
- a charge pump having a continuously variable charge pump current and for generating positive and negative output current levels whose magnitude depend on the magnitude of the charge pump current;
- a current controlled oscillator having an input current determined by the output current levels generated by the charge pump;
- and
- a feedback circuit for generating said charge pump current in response to said input current of said current controlled oscillator such that said charge pump current varies proportionally with to said input current,
- wherein said feedback circuit insures that said charge pump current has a minimum value B, and wherein said value B insures that said charge pump current has a non-zero value, and
- wherein said feedback circuit insures that said input current is above a threshold A to cause an increase in said charge pump current.
3 more elements
A phase-locked-loop, comprising:
- a phase comparator for receiving first and second periodic signals and providing a phase difference signal corresponding to the amount by which the first signal leads or lags the second signal;
- a charge pump responsive to the phase difference signal for generating positive and negative current pulses;
- an accumulator for accumulating the charge of the positive and negative current pulses and for generating a voltage indicative of the accumulated charge;
- a voltage-to-current converter for converting said voltage into a control current;
- a current controlled oscillator which generates said second signal at a frequency determined by said control current;
- and
- a feedback circuit having said control current as an input and having as an output a charge pump current which determines the magnitude of said positive and negative current pulses generated by said charge pump,
- wherein said feedback circuit insures that said charge pump current has a minimum value B, and wherein said value B insures that said charge pump current has a non-zero value, and
- wherein said feedback circuit insures that said control current is above a threshold A to cause an increase in said charge pump current.
6 more elements
Dependencies are inferred from the claim text.