Modified Doherty Transmit Architecture Employing Digital Signal Synthesis for Wideband RF Communication

This Small Business Innovation Research (SBIR) Phase I project proposes to demonstrate a Radio Frequency (RF) transmitter capable of groundbreaking performance for wireless infrastructure applications. Significant performance gains are expected from three main innovations in this highly-digital transmitter. First, building on the Doherty Power Amplifier (PA), a unique method of optimal digital synthesis of the RF drive signals is proposed; no analog upconversion, power-split and phase adjustment are needed. Digital signals drive a Doherty PA with modified bias, achieving higher efficiency than conventional designs. Second, efficiency and linearity are further improved over wide bandwidth (BW) by predistorting the digitized RF waveform directly. Third, a modular PA implementation is introduced, which is adaptively reconfigured to optimize the overall power efficiency with varying load. The design goals of the proposed work are: wide BW (100MHz), widely programmable carrier frequency (2.3-2.8GHz), high linearity (better than -65dBc), high output power (200W) and excellent average efficiency (>60% at 10dB backoff). Analysis comparing the proposed PA to a conventional design shows average efficiency improvements of over 10% for maximum average power and up to 100% for 6dB backed off average power; the output power and average power gain are enhanced by 11% and 4