Li-ion battery operated power amplifier MMICs utilizing SrTiO3 capacitors and heterojunction FETs for PDC and CDMA cellular phones

Highly efficient two-stage 1 W power amplifier MMICs utilizing SrTiO3 capac itors and Si-doped AlGaAs/InGaAs/Si-doped AlGaAs FETs have been developed f or Li-ion battery operated digital cellular phones. For the personal digita l cellular (PDC) applications, a power amplifier MMIC with 2.0 x 2.4 mm(2) area includes all bias and matching circuits. The MMIC delivered a 950 MHz pi/4-shifted QPSK output signal power (P-out) of 0.8 W (29.0 dBm), a power- added efficiency (PAE) of 30% and an associated gain (G(a)) of 26.4 dB with an adjacent channel leakage power ratio (ACPR) of -50.5 dBc at 50 kHz off- center frequency under 3.4 V drain bias operation. The power performance sh owed good agreement with a simulated one when series resistances in the out put matching circuit and the drain bias circuit for the second-stage FET we re taken into account. When the circuits were removed from the MMIC, it exh ibited PAE of 42.4% and P-out of 1.0 W (30.0 dBm) with G(a) of 29.8 dB at t he PDC criteria. These results revealed that a low loss in the output passi ve circuits of a power amplifier MMIC is essential. Then, a power amplifier MMIC for the IS-95 application at 840 MHz was designed and evaluated witho ut the output circuit. The MMIC with 2.0 x 1.5 mm(2) area delivered P-out o f 0.93 W (29.7 dBm), PAE of 48.6% and G(a) of 28.4 dB with ACPR of -42 dBc at 0.9 MHz off-center frequency under 3.5 V operation. Even operated at a r educed supply voltage of 1.2 V, a high PAE of 46.9% was obtained. These res ults indicate that the developed power amplifier MMICs and its approach are promising for small-size and lightweight digital cellular phones with long talk time. (C) 1999 Elsevier Science Ltd. All rights reserved.