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:
Feb. 11, 1997
Filed:
Mar. 29, 1994
Stuart M Feeney, Cupertino, CA (US);
P-Com, Inc., Santa Clara County, CA (US);
Abstract
An automatic frequency control circuit measures the deviation in frequency of a selected signal from a reference frequency and when the deviation exceeds a selected threshold which is variable, steps the frequency of the selected signal back to the proper frequency. The selected signal is typically an intermediate frequency (IF) signal in a radio receiver. For detection of frequency deviation, an exclusive OR (EX-OR) circuit receives a reference signal having a frequency proportional to a desired IF carrier frequency and an input signal having a frequency proportional to an actual IF frequency. A divider coupled to a voltage controlled oscillator (VCO) used in demodulation of the IF signal provides the input signal. An output signal of the EX-OR circuit includes a component with a frequency proportional to the difference between the actual and desired IF frequencies. A low pass filter isolates that component, and a charge pump generates a control voltage proportional to the frequency of that component. A comparison of the control voltage and the threshold determines whether the actual IF frequency should be changed.