US 11,815,552 B2
Clock frequency monitoring device and clock frequency monitoring method
Takaaki Hisashima, Tokyo (JP); Hiroki Sakuma, Tokyo (JP); Kaoru Arai, Tokyo (JP); Ryuta Sugiyama, Tokyo (JP); Shunichi Tsuboi, Tokyo (JP); Osamu Kurokawa, Tokyo (JP); and Kazuyuki Matsumura, Tokyo (JP)
Assigned to Nippon Telegraph and Telephone Corporation, Tokyo (JP)
Appl. No. 17/267,161
Filed by Nippon Telegraph and Telephone Corporation, Tokyo (JP)
PCT Filed Jul. 16, 2019, PCT No. PCT/JP2019/027839
§ 371(c)(1), (2) Date Feb. 9, 2021,
PCT Pub. No. WO2020/031623, PCT Pub. Date Feb. 13, 2020.
Claims priority of application No. 2018-150005 (JP), filed on Aug. 9, 2018.
Prior Publication US 2021/0302499 A1, Sep. 30, 2021
Int. Cl. G06F 1/12 (2006.01); G01R 31/317 (2006.01); H03K 5/00 (2006.01); H03K 5/1252 (2006.01); H03K 5/26 (2006.01)
CPC G01R 31/31726 (2013.01) [G06F 1/12 (2013.01); H03K 5/00006 (2013.01); H03K 5/1252 (2013.01); H03K 5/26 (2013.01)] 6 Claims
OG exemplary drawing
 
1. A clock frequency monitoring apparatus that recovers a synchronous clock synchronized with a first input clock and monitors a frequency of a second input clock that is to be frequency-synchronized with the first input clock, the clock frequency monitoring apparatus comprising:
a first phase comparator configured to compare a phase of the synchronous clock or a first frequency-divided clock obtained by frequency-dividing the synchronous clock with a phase of the first input clock;
a first filter configured to low-pass filter an output signal of the first phase comparator;
an oscillator configured to generate the synchronous clock having a frequency corresponding to an output signal of the first filter;
a second phase comparator configured to compare a phase of the synchronous clock or the first frequency-divided clock with a phase of the second input clock;
a second filter configured to low-pass filter an output signal of the second phase comparator; and
a determiner configured to determine that the frequency of the second input clock is abnormal when a variation amplitude of an output signal of the second filter is equal to or more than a predetermined range.