United States Patent 7,483,500
Takatz , et al. January 27, 2009
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Narrowband gain control of receiver with digital post filtering
Abstract
An Automatic Gain Control (AGC) circuit as used in a digital receiver that utilizes a main loop filter that is of a relatively wide bandwidth. A pre-filter, wideband variance is determined from the input digital signal, and a post-filter, narrowband variance is also determined. The wideband and narrowband variances are then compared to determine if the wideband signal power indicates a variance level that is too great to permit normal loop operation. By reapplying this difference in the power levels to the filter output as needed, such as by a scaling operation, the loss in dynamic range is effectively recovered. In a preferred embodiment, an adjustable gain input amplifier feeds an intermediate frequency (IF) signal to an analog-to-digital converter (ADC). The digitized IF signal is then down-converted to a baseband frequency and subjected to digital filtering. A narrowband sample variance (P.sub.N) of the digitally filtered (narrowband) data is then determined. A wideband sample variance (P.sub.W) is also taken from the raw ADC output data over the same period as the time period used for P.sub.N. In the presence of out-of-band signal components, P.sub.W will be quite different from P.sub.N. This difference indicates a desired proportional difference in a control voltage or a gain backoff amount.
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Inventors: Takatz; Mark J. (Melbourne, FL), Keel, Jr.; Alton S. (Hellam, PA), Haenggi; Stefan (Melbourne Beach, FL)
Assignee: IPR Licensing, Inc. (Wilmington, DE)
Appl. No.: 11/399,224
Filed: April 6, 2006
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Related U.S. Patent Documents
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Application Number Filing Date Patent Number Issue Date
09847056 May., 2001 7046749
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Current U.S. Class: 375/345 ; 375/316; 455/136; 455/138; 455/234.1; 455/239.1; 455/245.1; 455/247.1
Current International Class: H04L 27/08 (20060101)
Field of Search: 375/316,345 455/136,138,239.1,245.1,247.1,234.1
