42% high-efficiency two-stage HBT power-amplifier MMIC for W-CDMA cellular phone systems

This is the first paper to report on a high-efficiency two-stage heterojunction-bipolar-transistor power-amplifier monolithic microwave integrated circuit (MMIC) for 1.95-GHz wide-band code-division multiple-access (W-CDMA) cellular phone systems. Power amplifiers for W-CDMA systems are required to operate at high efficiency and high linearity over a wide range of output power levels. To obtain high efficiency at low output power (P_out) as well as at the required maximum P_out and obtain a high linearity at the maximum P_out, we chose near-class-B operation. To improve linearity at a medium P_out range, we suppressed the gain distortion resulting from near-class-B operation by using an adaptive biasing technique. The MMIC exhibited a power-added efficiency of 42%, the highest ever reported, a gain of 30.5 dB, and an adjacent channel leakage power ratio at a 5-MHz offset frequency of -38 dBc at a P_out of 27 dBm under a supply voltage of 3.5 V with 3.84-Mcps hybrid phase-shift keying modulation