Analog implementation of spread spectrum frequency modulation in a programmable phase locked loop (PLL) system
AssigneeAltera Corporation
InventorsGregory W. Starr, Wanli Chang
Life of this patent
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Abstract
A PLL circuit is described. The PLL circuit includes: a signal generator; and a spread spectrum modulator coupled to the signal generator, where the spread spectrum modulator receives a control voltage as an input and provides a spread spectrum control voltage to the signal generator in response to the control voltage. In one embodiment, the spread spectrum modulator includes at least one selector, where the at least one selector selects a plurality of voltage levels that correspond to a spread mode and percentage of spread for the spread spectrum modulator.
Claims11
A phase locked loop circuit including:
- a signal generator;
- and
- a spread spectrum modulator coupled to the signal generator, the spread spectrum modulator including at least one selector, wherein the at least one selector selects from at least one of a plurality of spread modes and percentages of spread for the spread spectrum modulator.
A digital system including a programmable logic device having a phase locked loop circuit including:
- a signal generator;
- and
- a spread spectrum modulator coupled to the signal generator, the spread spectrum modulator including at least one selector, wherein the at least one selector selects from at least one of a plurality of spread modes and percentages of spread for the spread spectrum modulator.
A programmable logic device including a phase locked loop circuit including:
- a signal generator;
- and
- a spread spectrum modulator coupled to the signal generator, the spread spectrum modulator including at least one selector, wherein the at least one selector selects from at least one of a plurality of spread modes and percentages of spread for the spread spectrum modulator.
A method of providing an output clock signal, the method comprising:
- spreading a control voltage using an analog spread spectrum modulator that includes a selector to provide a spread spectrum control voltage;
- selecting in the selector at least one of a spread rate and percentage of a spread of the spread spectrum control voltage;
- and
- generating an output clock signal in response to the spread spectrum control voltage.
Dependencies are inferred from the claim text.