Directional Coupler Boosts GSM Power Amp

Designed for GSM cell phones of all types, the quad band ADL5552 X-PA power-amplifier chip covers the European 900-MHz, U.S. 850-MHz, European DCS 1800-MHz, and U.S. PCS 1900-MHz bands. It also supports GPRS to level 12. The amplifier circuitry's gallium-arsenide (GaAs) heterojunction bipolar transistors (HBT) operate class AB and feature a 55% efficiency. Within its architecture, one amplifier is used for the 850/900-MHz bands and the other for the 1800/1900-MHz DCS/PCS bands. An internal directional coupler in both samples the output power and provides feedback control of output power. The X-PA architecture's logarithmic detection provides precise exponential (linear-in-dB) output power control over a 40-dB range. The ADL5552 operates with a 2.9- to 4.5-V dc supply and comes in an 8- by 6- by 1.4-mm LCC package. Pricing is $3 per unit in 10,000-unit quantities.

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