Direct Digital Predistorter for Linearization of RF Transmitter Power Amplifiers

"HYPRES, in collaboration with University of Rochester, proposes to develop a novel architecture for rf transmitters. A digital predistortion scheme will be developed for direct manipulation of the rf waveform at GHz frequencies, using the high-speeddigital signal processing capability of low-temperature superconductor (LTS) electronics. This digital-RF predistorter will be integrated with a quantum-accurate digital-to-analog converter (DAC) to achieve performance levels that cannot be achieved byconventional baseband predistortion techniques. We propose to generate the rf waveform from an oversampled digital bit stream following up-conversion of baseband signals, all in the single flux quantum (SFQ) digital domain. The predistortion is performeddirectly on the SFQ digital bit-stream. HYPRES has already developed key components for a digital receiver for direct digitization of rf waveforms. Following the design of the predistorter circuit architecture in Phase I, HYPRES will develop, fabricate anddemonstrate LTS integrated circuits for the digital-RF transmitter in Phase II. This will lead to the development and commercialization of a line of digital-RF transceiver products for the military and the commercial markets. Through better linearizationof power amplifiers the spectral purity of the transmit signal is enhanced, yielding benefits, such as accurate target characterization and discrimination, elimination of false targets and extended range for radar systems. The amplifiers can also be mademore linear over a broader bandwidth, enabling multi-carrier, multi-function (radar, communications, electronic warfare) operation. Finally, the ability to linearize strongly nonlinear amplifier characteristics allow the use of cheaper, more efficientamplifiers, resulting in significant savings in procurement cost as well as operational expenses. Theis technology will not only have a major impact on US military technology but also be extremely valuable for commercial wireless communication systems."