Research into Memory Effects Compensation and Crest Factor Reduction for Multicarrier Microwave Power Amplifiers, 10-9496

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Principal Investigators
Gary L. Ragsdale
Michael J. Magee
Myron L. Moodie
Michael E. Pilcher
Travis Thompson

Inclusive Dates:  07/01/04 - Current

Background - Combining several carrier signals within a transmitter's power amplifier creates large variations in amplifier output power, a condition described as high peak to average ratio (PAR). Under high average power output and high PAR, the amplifier will experience rapid temperature variations. A high PAR may also cause variations in the amplifier DC supply voltage. The amplifier temperature and DC voltage variations, in turn, induce variations in the amplifier's gain characteristic, called memory effects. Amplifier memory effects generate prohibited adjacent channel and alternate channel interference unless adequate steps are taken to compensate for the gain variations.

Approach - A more efficient, highly linear microwave amplifier would lower the cost of constructing and operating high-power transmitters used in multicarrier broadcast applications such as third-generation cellular telephone base stations, high-definition television transmitters, military jamming transmitters, and radio-frequency test systems. Memory effects compensation (MEC) and crest factor reduction (CFR) are promising areas of research that can lead to microwave amplifier performance.

Recent developments in high-speed integrated circuits make it possible to implement MEC and CFR techniques within digital predistortion application-specific integrated circuit (ASIC) and field programmable gate array chips (FPGA.). The digital predistortion system can correct amplifier gain anomalies if the system is controlled by an appropriate compensation method. Basic research indicates that the proper application of integrated circuits for MEC and CFR, and mathematical methods can simultaneously compensate for amplifier memory effects and reduce the amplifier output PAR, thereby stabilizing the amplifier gain characteristic and reducing prohibited radio-frequency interference. This project will create a multicarrier digital predistortion system that demonstrates the benefits of the new SwRI MEC and CFR techniques.

Accomplishments - Because the project was only recently initiated, no accomplishments have been completed to date.

A graph demonstrating memory effects compensation with crest factor reduction

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