Li-ion battery operated power amplifier MMICs utilizing SrTiO 3 capacitors and heterojunction FETs for PDC and CDMA cellular phones

Abstract

Highly efficient two-stage 1 W power amplifier MMICs utilizing SrTiO 3 capacitors and Si-doped AlGaAs/InGaAs/Si-doped AlGaAs FETs have been developed for Li-ion battery operated digital cellular phones. For the personal digital cellular (PDC) applications, a power amplifier MMIC with 2.0×2.4 mm 2 area includes all bias and matching circuits. The MMIC delivered a 950 MHz π/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 showed good agreement with a simulated one when series resistances in the output matching circuit and the drain bias circuit for the second-stage FET were taken into account. When the circuits were removed from the MMIC, it exhibited PAE of 42.4% and P out of 1.0 W (30.0 dBm) with G a of 29.8 dB at the PDC criteria. These results revealed that a low loss in the output passive 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 without the output circuit. The MMIC with 2.0×1.5 mm 2 area delivered P out of 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 reduced supply voltage of 1.2 V, a high PAE of 46.9% was obtained. These results indicate that the developed power amplifier MMICs and its approach are promising for small-size and lightweight digital cellular phones with long talk time.