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:
Dec. 05, 1995
Filed:
Sep. 14, 1992
Brian F Reilly, Hillsboro, OR (US);
Clifford A Davidow, Portland, OR (US);
NEC America, Inc., Melville, NY (US);
Abstract
A local clock system uses a numerically controlled oscillator referenced to a stable oscillator to generate local clock signals under microprocessor control. Two feedback loops provide inputs to the microprocessor for maintaining synchronization with the external clock reference; a frequency locked and a phase-locked loop. The relatively wide-band frequency-locked loop is used to acquire initial synchronization with the external clock reference when the external clock is restored after having been lost or is switched to a new source. The phase-locked loop has a narrow bandwidth and provides a large attenuation of any jitter on the incoming reference with a resultant low output jitter. The microprocessor provides a hold-over operation upon loss of the external clock reference and when the external reference is restored it slowly adjusts the output clock frequency to match that of the reference, limiting the rate of adjustment so as not to exceed a specified allowable jitter in the local clock output.