US 7,379,725 B2
LNA gain adjustment in an RF receiver to compensate for intermodulation interference
Hong Shi, Redondo Beach, Calif. (US)
Assigned to Broadcom Corporation, Irvine, Calif. (US)
Filed on Sep. 19, 2006, as Appl. No. 11/523,332.
Prior Publication US 2007/0010224 A1, Jan. 11, 2007
Int. Cl. H04B 1/10 (2006.01)
U.S. Cl. 455—296  [455/226.2; 455/295; 455/302] 4 Claims
OG exemplary drawing
 
1. A method comprising:
receiving a radio frequency signal at an input of a low noise amplifier during a guard period when a carrier corresponding to a signal of interest is not present;
measuring wideband signal strength indication (RSSI_A) at an output of a mixer, the mixer coupled to receive an output of the low noise amplifier;
determining if mixer non-linearity is present based upon the wideband signal strength indication;
reducing gain of the low noise amplifier if mixer non-linearity is present, until the mixer is no longer driven into non-linearity;
determining if wideband signal strength indication exceeds a predetermined threshold that causes the mixer to operate in an upper range of mixer operation;
measuring narrowband signal strength indication (RSSI_B) after band pass filtering the output of the mixer, if wideband signal strength indication exceeds the predefined threshold;
determining if intermodulation interference is present using the narrowband signal strength indication;
optimizing a signal-to-interference ratio of the mixer by setting the gain of the low noise amplifier to have the mixer operate within its linear region of operation, if intermodulation interference is detected; and
setting the gain of the low noise amplifier so that narrowband signal strength indication exceeds a predetermined minimum, in which a combination of wideband signal strength indication and narrowband signal strength indication based gain adjustments of the low noise amplifier is employed to compensate for intermodulation interference.