The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Mar. 21, 1995
Filed:
Mar. 18, 1993
Yutaka Awata, Kawasaki, JP;
Nobukazu Koizumi, Kawasaki, JP;
Yasuo Ohtomo, Kawasaki, JP;
Mitsuo Kakuishi, Kawasaki, JP;
Fujitsu Limited, Kanagawa, JP;
Abstract
The invention provides a digital PLL circuit wherein the integration time constant of a random walk filter can be varied adaptively in response to a frequency error. A master clock signal having a frequency equal to N (integral number) times that of an input clock signal is normally divided by N by a divider, and the division output of the divider and the input clock signal are compared in phase with each other by a phase comparator. The dividing ratio of the divider is temporarily varied in accordance with a result of the comparison so as to make the phases of the division output and the input clock signal coincide with each other to establish synchronism between them. A variable step number random walk filter is interposed between the phase comparator and the divider and has a selectively settable integration time constant, and an integration time constant setting circuit varies the step number of the random walk filter in accordance with information of a last phase controlling direction or directions and information of a phase controlling direction at present to vary the integration time constant of the random walk filter.