Frequency synthesizer having a more versatile and efficient fractional-N control circuit and method using vector values
AssigneeCypress Semiconductor Corporation
InventorShuliang Li
Life of this patent
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Abstract
A frequency synthesizer is provided having a fractional-N control circuit and method that can selectively apply any fractional ratio to a frequency divider within the feedback loop of a PLL. A special digital delta-sigma modulator can be implemented as the control circuit and can receive any arbitrary numerator and denominator value, or their arithmetic combination, or a positive and negative vector values used by the modulator to achieve an average fractional division. Both the numerator and denominator (or the positive and negative vectors) can be chosen based on any integer value to achieve a more optimal, higher frequency resolution and efficient fractional-N control circuit and methodology thereof.
Claims19
A modulator circuit, comprising:
- a multiplexer coupled to receive a positive vector value and a negative vector value;
- and
- an adder coupled to receive an output from the adder and either the positive vector value or the negative vector value depending on a sign output from the adder.
A circuit for producing a signal of selectable frequency, comprising:
- a modulator;
- and
- a phase-locked loop having a divider that fractionally divides a frequency of the signal based on a most significant bit pattern of a sequence of a signed binary number output from the modulator to the divider.
A method of modifying a frequency of a signal, comprising:
- modulating a bit pattern from a sequence of signed binary numbers by extracting the signed binary numbers from a digital word and extracting the bit pattern from the most significant bit output of the digital word;
- defining a ratio of logic values within the bit pattern by setting either a positive vector value corresponding to a positive delta change between successive signed binary numbers or a negative vector corresponding to a negative delta change between successive signed binary numbers;
- and
- dividing the frequency of the signal based on the defined ratio.
Dependencies are inferred from the claim text.