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:
May. 16, 2000
Filed:
Apr. 21, 1998
Robert Keith Douglas, San Diego, CA (US);
Uniden San Diego Research & Development Center, San Diego, CA (US);
Abstract
A system for compensating for reference frequency drift in a communications system. The inventive system includes a frequency source for providing a reference frequency. An error determination circuit determines if the reference frequency is within a predetermined range of a desired reference frequency and provides an error signal in response thereto. A frequency correction circuit steps the reference frequency up and/or down by a predetermined amount in response to the error signal until the reference frequency is within the predetermined range of the desired reference frequency. In a specific embodiment, the predetermined amount is twice the short-term capture range of the reference frequency which corresponds to approximately four parts per million. The predetermined range is the short-term capture range or two parts per million. The predetermined range is dependent upon the reference frequency band in which the receiver can successfully receive and decode the receive signal. The frequency source includes a voltage-controlled temperature-compensated crystal oscillator (VC-TCXO). The error determination circuit is a processor connected to the receiver. The processor includes a short-term frequency drift detector/compensator that generates a first control voltage input to the VC-TCXO for correcting the reference frequency in response to the error signal. The processor further includes a digital signal processing circuit for processing signals received from the receiver and determining the error signal in response thereto. The frequency correction circuit includes a long-term frequency drift detector/compensator that generates a second control voltage that is input to the VC-TCXO for correcting the reference frequency in response to the signal. In a more specific embodiment, the long-term frequency drift detector receives a correction signal from the short-term frequency drift detector indicating if the short-term frequency drift detector was successful in adjusting the reference frequency to the desired reference frequency.