Spread spectrum clock generation
First Claim
1. A spread spectrum clock generation system comprising:
- a digitally controlled phase locked loop (PLL) circuit; and
a digital frequency profile generator connected to the digital control input of said PLL circuit.
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Abstract
The present disclosure provides a spread spectrum clock generation system having a digitally controlled phase locked loop (PLL) and a digital frequency profile generator to create a near optimal frequency modulation profile for the purpose of achieving spectral flatness in the output frequency modulated clock. The circuit is combined with a multilevel error feedback noise shaping structure that provides the required noise transfer function for the quantization noise but maintains a unity gain all pass signal transfer function. This arrangement offers minimal degradation of the in-band signal-to-noise ratio (SNR) at the cost of higher out-of-band noise.
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Citations
20 Claims
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1. A spread spectrum clock generation system comprising:
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a digitally controlled phase locked loop (PLL) circuit; and a digital frequency profile generator connected to the digital control input of said PLL circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for generating a spread spectrum clock, the method comprising:
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providing a digitally controlled phase locked loop (PLL) circuit; and modulating the frequency generated by said PLL circuit by applying a controlled modulating signal to the digital control input of said PLL circuit. - View Dependent Claims (11, 12, 13)
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14. For use in spread spectrum clock generation, a system for providing center spread and down spread operating modes, the system comprising:
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a digitally controlled phase locked loop (PLL) circuit; and a digital frequency profile generator connected to the digital control input of said PLL circuit, wherein said digital frequency profile generator comprises; a triangular wave generator; and a second order sigma-delta modulator (SDM) connected to the output of said triangular wave generator wherein said triangle wave generator comprises a synchronizer to synchronize input asynchronous amplitude and frequency values to an internal system clock. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification