Spread spectrum clock generator, spread spectrum clock generating method, and circuit, image reading device and image forming apparatus using the spread spectrum clock generator
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United States of America Patent
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Apr 9, 2013
Grant Date -
Feb 3, 2011
app pub date -
Jun 8, 2010
filing date -
Jul 30, 2009
priority date (Note) -
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Abstract
The spread spectrum clock generator (SSCG) includes a phase comparator detecting phase difference between input clock and feedback clock; a charge pump supplying current depending on the phase difference; a loop filter converting the current to smoothed voltage; a voltage controlled oscillator generating a spread spectrum clock signal depending on the smoothed voltage; and a modulation signal generator generating modulation signal having amplitude depending on a modulation width set value. The SSCG further includes a modulation width detector detecting modulation width of the spread spectrum clock signal while comparing the modulation width with a modulation width target value to update the modulation width set value to narrow difference between the detected modulation width and the modulation width target value, followed by feeding back the updated modulation width set value to the modulation signal generator.
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