UNDERSTANDING HANDSET POWER-AMPLIFIER TRADE-OFFS

DESIGNING a cellular telephone or wireless transceiver requires select ion of a final RF power amplifier that will provide a reliable RF sign al to the antenna under varying battery conditions, and with minimal b attery drain during standby. The designer must also consider economic trade-offs. Will a gallium-arsenide (GaAs) amplifier, for example, wit h higher unit cost than a silicon-bipolar amplifier, provide better pe rformance, and offer simpler bias requirements. What is the harmonic c ontent delivered to the antenna in each case? A silicon power module m ay work effectively, but will it be more expensive than a predriver wi th a silicon bipolar output stage? What follows are some straightforwa rd guide lines to help wireless handset designers effectively select p ower amplifiers.