A 3.3V, 1W GaAs One-Chip Power Amplifier MMIC for Cellular Phones

Abstract

ABSTiRACA 900-MHz-band 1W one-chip power amplifier MMIC, which operates at the low-supply voltage of 3.3 V and includes all bias and output matching circuits, has been developed for cellular phones. It is capable of delivenrng output power-over 1.1 W with a power added efficiency of 43% at 3.3 V. With its extremely small chip size of 2.5 mm x 3.48 mm, it is less than one fifth the size of previously reported multi-chip ICs (MCICs). This new MMIC, the characteristics of which are compared with those of the existing MCICs, can be expected to contribute to the realization of smaller, lighter-weight cellular phones. IIJTRQDUCTIONThere is a strong demand for the power amplifiers of cellular phones to operate on lower supply voltages, for a smaller chip size,-and for lower costs. A reduction in the number of cells in the batteries achieved by low-voltage operation would enable a substantial reduction in the volume and weight of telephones. Because, for example, an amplifier operating at 3.6 V or less would require just one lithium (Li+) battery, many vendors are concentrating on the development of power amplifiers operating at 3.Several works have already reported amplifier MCICs and hybnrd ICs with 1W output for cellular phones-operating in the 900-MHz band used in Japan [3], [4]. However, these devices only;operate at 5.8 V or 4.7 V, though there have been reports of 1W amplifier ICs that will operate at 3.6 V or less [5], [6]. However, from the viewpoint of high volume production, MMICs are preferable to MCICs because of the lower testing costs and assembly costs. This paper reports a newly developed one-chip power amplifier MMIC with a saturated output of more than 1.1 W operating at 3.3 V. We also compare the characteristics of this IC with the existing MCICs for cellular phones to clarify the respective merits and demerits. EELDESIQN A low-voltage power MESFET using optimized fabrication process technology and device dimensions has already been developed [6]. Figure 1 is a schematic cross-section of this MESFET, which features an aluminum gate of 0.5 pm length and recess etching process. By reducing the gate-to-source and gate-to-drain length and optimizing the doping concentration of epitaxial active layer, it has been possible to achieve I-V charactenrstics of a low-knee voltage of 1 V and a highbreakdown voltage of 14 V or more. These results are important for efficient operation with lowsupply voltages.The typical drain saturation current, Idss, and pinch-otf voltage, Vp, are 300 mA/mm and -2.2 V, respectively. In the FF1' with a gate-width of 2.4 mm, load-pull measurement of the fundamental frequency and 2nd-harmonic at Vr3.3 V and fo=950 MHz revealed a saturated output power of 23.6 1066