A clever distributed circuit design helps overcome the power limitations of conventional silicon CMOS processing in providing high GSM handset power levels with generous efficiency.
Amplifier specifiers involved with selecting products for GSM cellular-telephone designs have learned to choose from a substantial list of module solutions. These modules are accompanied by one or two amplifier chips and a power-control IC, and sometimes still require external circuitry for DC blocking and impedance matching. In contrast, the Si4300 GSM/GPRS power amplifier (PA) from fabless-semiconductor company Silicon Laboratories (Austin, TX) is a complete monolithic amplifier integrated circuit (IC), a single device that includes all the functions between a GSM handset transceiver and the antenna/switch module. Operating in both the GSM 900 (880-to-915-MHz) and DCS 1800 (1710-to-1785-MHz) bands, the IC includes the amplifiers, harmonic filtering, complete power-control circuitry, and impedance matching and requires no external discrete components.
Unlike most (GaAs) GSM handset PAs, the Si4300 (see figure) is made with a standard 0.35-µm silicon CMOS process. By using a novel circuit design employing distributed device stages, the Si4300 can achieve the high voltages needed for high-gain amplification in CMOS. Unlike GaAs-based PA modules which can measure 7 × 10 mm or more, the Si4300 is supplied as a single die in a compact 3.9 × 6.4 mm ceramic package. Like the GaAs PA modules, the Si4300 is designed for voltages from +3.0 to +5.5 VDC.
The Si4300 features a GSM output-power level of +34.7 dBm and DCS output-power level of +32.3 dBm, while achieving typical power-added efficiency of better than 50+ percent. Silicon Laboratories, Inc., 4635 Boston Lane, Austin, TX 78735; (512) 416-8500, (877) 444-3032, FAX: (512) 464-9444, e-mail: PAinfo@silabs.com, Internet: www.silabs.com.