Cellular handset designers yearn for amplification that is compact and simple to use. The +3.5-VDC model RF3133 PowerStar™ power-amplifier (PA) module from RF Micro Devices (Greensboro, NC) may just be the ideal PA solution, since it measures just 7 × 10 × 1.4 mm with integral power control. Based on AlGaAs/GaAs HBT technology, the four-band PA achieves 55-percent power-added efficiency (PAE) with +35 dBm output power in the Global Systems for Mobile Communications (GSM) band and 50-percent PAE with +33 dBm output power in the digital-communications-services (DCS)/ personal-communications-services (PCS) bands.
The PA's architecture is a direct extension of earlier work with integrated collector power control. Like the company's three-band model RF3110, the RF3133 provides 35-dB power-control range, but across four wireless bands. Unlike traditional PA modules, in which matching and bypass functions are implemented with discrete surface-mount components, the RF3133 (see figure) integrates all matching and bypassing components on the chip. Integration of these components permits a priori modification of reactance values based on in situ measurement during part fabrication. Furthermore, rather than a random distribution of part values and quality factors (Qs) inherent with discrete parts, capacitor values vary in unison, which stabilizes the impedance presented to the PA.
The integrated power-control circuitry eliminates the need for additional components, such as directional couplers, detector diodes, and power-control application-specific integrated circuits (ASICs), shrinking the area of the PA printed-circuit board (PCB), reducing overall PA parts costs by $0.90, and even saving the calibration time needed to tune the power-control function (at a cost of about $0.04/second of calibration time). The power-control architecture utilized is accurate and repeatable over process variation. This accuracy and repeatability facilitates faster phone calibration. The measurement uncertainty in the test equipment is greater than the process variation in the PA output power versus Vramp (the power-control pin) with considerable margin. The phone now can be calibrated at a single point, or the calibration can be eliminated. A single-point calibration on a phone with an RFMD PA can save $0.30 to $1.10 per phone. RF Micro Devices, 7628 Thorndike Rd., Greensboro, NC 27409; (336) 664-1233, FAX: (336) 931-7454, Internet: www.rfmd.com.