1. Field of the Invention
The present invention relates to a receiver for a radio communication system, and in particular, to a receiver capable of suppressing intermodulation distortion signals and a method for operating the same.
2. Description of the Related Art
In a mobile communication terminal, an intermodulation distortion signal contained in a frequency band of a received RF (Radio Frequency) signal deteriorates a reception sensitivity. If the intermodulation distortion signal is greater in strength than the received RF signal, the receiver can barely detect the received signal, thus causing deterioration of the reception sensitivity. This intermodulation distortion problem is at issue in a radio communication terminal, especially, in an IS-95 dual mode (CDMA (Code Division Multiple Access) & AMPS (Advanced Mobile Phone Service)) cellular phone. For instance, in a mobile radio communication system such as a CDMA cellular system, undesired interferers (or interference signals) caused by the AMPS are intermodulated with each other, thereby generating a third order intermodulation distortion signal (i.e., the third harmonic intermodulation distortion signal). When the intermodulation distortion signal is considerably greater in strength than the CDMA signal, the reception sensitivity for the CDMA signal is lowered drastically. One process for improving the quality of a received signal in a radio receiver operating according the IS-95 standard is based on the combination of the received signal strength and signal-to-noise ratio, as contemplated by U.S Pat. No. 5,758,271 to Randall W. Rich et al. entitled Apparatus And Method for Optimizing The Quality Of A Received Signal In A Radio Receiver, incorporated herein by reference. U.S Pat. No. 5,697,081 to Robert L. Lyall, Jr. et al. entitled Intermodulation Distortion Reduction Circuit Utilizing Variable Attenuation contemplates a process wherein a variable attenuator, responsive to received signal strength in a receiver, provides variable attenuation to reduce intermodulation distortion according to an IS-98 standard. Reduction of intermodulation distortion is also contemplated by U.S. Pat. No. 5,564,094 to George C. Anderson et al. entitled Radio Receiver Providing Reduced Intermodulation Distortion; U.S. Pat. No. 5,001,776 to Edward T. Clark entitled Communication System With Adaptive Transceivers To Control Intermodulation Distortion; and U.S. Pat. No. 5,170,392 to Kenneth B. Riordan entitled Intermodulation Compensation In A Receiver.
USPTO Backgrounds
USPTO Backgrounds