Spread spectrum type clock generation circuit for improving frequency modulation efficiency
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United States of America Patent
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Jul 8, 2008
Grant Date -
Aug 18, 2005
app pub date -
Jan 26, 2005
filing date -
Feb 18, 2004
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Abstract
The present invention provides a spread spectrum type clock generation circuit whose EMI for peripheral equipment is reduced. The clock generation circuit comprises a phase-locked loop circuit and a clock modulation circuit. The clock modulation circuit comprises a .DELTA..SIGMA. modulator, to frequency-modulate an output clock by modulating the frequency division number of a frequency divider in the phase-locked loop circuit by a digital circuit, and further comprises a modulation pattern controller for distributing the peak of a triangular waveform which is a modulation waveform generated by a modulation pattern generator to change the amplitude and the period thereof, thereby making it possible to eliminate dullness and distortion of a modulation waveform in a modulating method using a conventional analog circuit and to obtain an output clock having higher modulation efficiency than that in a case where a normal triangular waveform is employed in a conventional modulating method using a digital circuit.
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