Coarse tuning for fractional-N synthesizers
First Claim
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1. A fractional-N frequency synthesizer comprising:
- a phase lock loop (PLL); and
coarse tuning circuitry coupled to the PLL and adapted to control the PLL such that the PLL operates in an integer division mode during coarse tuning and a fractional-N division mode during normal operation, wherein the coarse tuning circuitry comprises divide value generation circuitry adapted to;
provide an integer divide value to a divider of the PLL when operating in the integer division mode; and
provide a fractional sequence of divide values to the divider of the PLL when operating in the fractional-N division mode,wherein the PLL comprises a controlled oscillator (CO) and the coarse tuning circuitry further comprises;
an M divider adapted to divide a reference signal from the PLL by a factor M to provide an divided reference signal; and
tuning logic adapted to;
compare a frequency of the divided reference signal and a frequency of a divided controlled oscillator (CO) signal during coarse tuning, wherein the divided CO signal is a CO signal from the CO divided by the integer divide value; and
provide a tuning curve control signal to select a tuning curve for a CO of the PLL based thereon to effect coarse tuning of the CO.
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Abstract
An improved coarse tuning process for fractional-N frequency synthesizers is provided. In general, a coarse tuning circuit controls a phase lock loop (PLL) of a frequency synthesizer such that the phase lock loop operates in an integer division mode during coarse tuning, thereby eliminating jitter due to fractional-N operation during coarse tuning. The coarse tuning circuit includes divide value generation circuitry that provides an integer divide value to an N divider of the PLL during coarse tuning and a fractional-N sequence to the N divider during fractional-N operation.
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Citations
32 Claims
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1. A fractional-N frequency synthesizer comprising:
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a phase lock loop (PLL); and coarse tuning circuitry coupled to the PLL and adapted to control the PLL such that the PLL operates in an integer division mode during coarse tuning and a fractional-N division mode during normal operation, wherein the coarse tuning circuitry comprises divide value generation circuitry adapted to; provide an integer divide value to a divider of the PLL when operating in the integer division mode; and provide a fractional sequence of divide values to the divider of the PLL when operating in the fractional-N division mode, wherein the PLL comprises a controlled oscillator (CO) and the coarse tuning circuitry further comprises; an M divider adapted to divide a reference signal from the PLL by a factor M to provide an divided reference signal; and tuning logic adapted to; compare a frequency of the divided reference signal and a frequency of a divided controlled oscillator (CO) signal during coarse tuning, wherein the divided CO signal is a CO signal from the CO divided by the integer divide value; and provide a tuning curve control signal to select a tuning curve for a CO of the PLL based thereon to effect coarse tuning of the CO. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method for coarse tuning a fractional-N frequency synthesizer comprising:
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providing an integer divide value to a divider of a phase lock loop (PLL) during coarse tuning, thereby controlling the PLL such that the PLL operates in an integer division mode during coarse tuning; providing a fractional sequence of divide values to the divider of the PLL during normal operation, thereby controlling the PLL such that the PLL operates in a fractional-N division mode during normal operation; dividing a reference signal from the PLL by a factor M to provide a divided reference signal; comparing a frequency of the divided reference signal and a frequency of a divided controlled oscillator (CO) signal during coarse tuning, wherein the divided CO signal is a CO signal from a CO of the PLL divided by the integer divide value; and providing a tuning curve control signal to select a tuning curve for the CO of the PLL based thereon to effect coarse tuning of the CO. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A method for coarse tuning a fractional-N frequency synthesizer comprising:
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providing an integer divide value to a divider of a phase lock loon (PLL) during coarse tuning thereby controlling the PLL such that the PLL operates in an integer division mode during coarse tuning; providing a fractional sequence of divide values to the divider of the PLL during normal operation, thereby controlling the PLL such that the PLL operates in a fractional-N division mode during normal operation; and determining the integer divide value based on the multiplication of a desired divide value of the fractional-N synthesizer and the factor M. - View Dependent Claims (28, 29)
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30. A circuit for coarse tuning a fractional-N frequency synthesizer comprising:
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a) divide value generation circuitry adapted to provide an integer divide value to a divider of a phase lock loop (PLL) when operating in an integer mode, and further adapted to provide a fractional sequence of divide values to the divider of the PLL when operating in a fractional-N mode, the mode of the divide value generation circuitry selected by a control signal; b) an M divider adapted to divide a reference signal from the PLL by a factor M to provide an divided reference signal; and c) tuning logic adapted to; i) provide the control signal such that the divide value generation circuitry operates in the integer mode during coarse tuning and in the fractional-N mode thereafter; and during coarse tuning, further adapted to; ii) compare a frequency of the divided reference signal and a frequency of a divided controlled oscillator (CO) signal during coarse tuning, wherein the divided CO signal is a CO signal from a CO of the PLL divided by the integer divide value; and iii) provide a tuning curve control signal to select a tuning curve for the CO based thereon to effect coarse tuning of the CO. - View Dependent Claims (31, 32)
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Specification