High-efficiency power characteristics for WCDMA applications of SiGe HBT devices using a novel form of base-bias resistance

We present SiGe heterojunction bipolar transistor (HBT) devices that exhibit highly efficient and linear power characteristics comparable to those of GaAs HBTs under wide-band code-division multiple-access (WCDMA) modulation for the first time. Two resistors in series are inserted in the base-bias current path of the device. One only conducts envelope-frequency components of the base current while the other also conducts DC. By adjusting the resistance values, the adjacent channel power ratio (ACPR) was significantly reduced over a wide range of output power levels without loss of efficiency. An optimized device with a total emitter area of 3390 /spl mu/m/sup 2/ exhibited 44% power-added-efficiency (PAE) and 27.3-dBm output power with ACPR of less than -40 dBc under WCDMA modulation at 1.95 GHz and 3.4-V bias voltage.