A dual-gain-mode high efficiency power amplifier for W-CDMA data communications

A dual-gain-mode power amplifier (PA) with a step attenuator (ATT) for W-CDMA data communications is described. The step ATT placed at the interstage of the two-stage amplifier gives a two gain step — a 0-dB thru state (high-gain mode) and a 14-dB attenuation state (low-gain mode). In addition, the ATT featuring a capacitor for phase discontinuity compensation can suppress a phase difference between the two states and also keeps good input return loss of the PA. The PA fabricated in a BiFET process integrates the two stage amplifier, its bias circuit, a reference voltage generator, and a bi-layer directional coupler on a 3 mm × 3 mm laminate. Measurements under a condition of a 824 MHz W-CDMA (R99) modulated signal and a 3.4 V supply voltage shows that the PA can achieve a power added efficiency (PAE) of 50% at output power (Pout) of 27.8 dBm in the high-gain mode. In the high- and low-gain modes, measured phase difference is as small as 7° and measured input return loss is well maintained at less than −10 dB. Due to good directivity, the integrated coupler with a coupling factor of −19.6 dB can keep a small detection error of less than 0.5 dB even under a load mismatching condition of 2.5∶1 VSWR.