SiGe-based Power Amplifier for CDMA Handset Circuitry

Technical progress in bringing SiGe heterojunction bipolar transistor (HBT) technology to reality has been exceptionally rapid. The first functional SiGe HBT was demonstrated in December 1987, only fifteen years ago. In this fifteen years, since the first demonstration of a functional transistor, SiGe HBT technology has emerged from the research laboratory, entered manufacturing on 200-mm wafers, and is poised to enter the commercial radio frequency (RF) and microwave market [1]. Since several years ago, efforts have been made in making SiGe HBT power amplifiers (PAs) for digital European cordless telephone (DECT) and Global System for Mobile Communications (GSM) handset transmission application. However, the output power of the DECT is relatively low (24dBm) and the linearity of the GSM is far less restrictive than that of CDMA (Code Division Multiple Access) [2]. To further improve the linearity and power added efficiency (PAE), people have recently designed SiGe HBTs with high f max and high breakdown voltage, and PA ICs with high PAE and relatively high acceptable linearity. Power HBT design targeting high breakdown voltage with low current density can be obtained by designing a thick and lightly doped collector layer, and a multifinger emitter configuration is required for high current density to reduce thermal effects. The specially designed SiGe HBTs used in CDMA handset PAs can have a breakdown voltage BV CE0 as high as 7.3V and 7 V, f max of 50 GHz and 55 GHz , current gain of 180 and 80 for Atmel SiGe technology and IBM SiGe technology respectively. Commercially available SiGe based CDMA PAs can have an output power of 28 dBm and power PAE over 35%. The acceptable linearity for specially designed circuitry can be as high as ACP~ 42dBc. Specially, this paper reports on the design and characterization of the SiGe HBT devices and SiGe PA circuitries for CDMA handset application.