US 9,813,068 B2
Spread spectrum clock generator, electronic apparatus, and spread spectrum clock generation method
Keiichi Iwasaki, Kanagawa (JP)
Assigned to RICOH COMPANY, LTD., Tokyo (JP)
Filed by Keiichi Iwasaki, Kanagawa (JP)
Filed on Oct. 1, 2015, as Appl. No. 14/872,236.
Claims priority of application No. 2014-204495 (JP), filed on Oct. 3, 2014; and application No. 2015-143581 (JP), filed on Jul. 21, 2015.
Prior Publication US 2016/0099719 A1, Apr. 7, 2016
Int. Cl. H03L 7/00 (2006.01); H03L 7/08 (2006.01); H03K 4/06 (2006.01); H03L 7/081 (2006.01); H03L 7/10 (2006.01); H03K 3/64 (2006.01); H03L 7/06 (2006.01); H03L 7/16 (2006.01); H03K 3/78 (2006.01)
CPC H03L 7/0805 (2013.01) [H03K 4/06 (2013.01); H03L 7/081 (2013.01); H03K 3/64 (2013.01); H03K 3/78 (2013.01); H03L 7/06 (2013.01); H03L 7/10 (2013.01); H03L 7/16 (2013.01)] 7 Claims
OG exemplary drawing
 
1. A spread spectrum clock generator, comprising:
a phase comparator to compare a reference clock with a feedback clock to obtain a comparison result;
a low-pass filter to pass a predetermined low-frequency component from a signal of the comparison result to obtain a filtered signal;
a phase lock loop including a voltage-controlled oscillator that generates an output clock whose frequency corresponds to the filtered signal;
a triangular wave controller to generate a triangular wave signal for frequency-modulating a spread spectrum clock based on the output clock;
a delay controller to generate the feedback clock by controlling delay of the output clock based on the triangular wave signal;
a first counter to count the output clock to output a first count value;
a second counter to count the reference clock to output a second count value; and
a phase error correction circuit to compare the first count value with the second count value for period that is a cycle or a multiple of the cycle of the frequency modulation and correct phase error of the output clock by modifying a shape of the triangular wave signal so that the first count value matches the second count value based on the comparison result.