Low ACPR Characteristics for WCDMA Applications of SiGe:C HBT Devices with Small Emitter Capacitance

摘要

We present C-doped SiGe (SiGe:C) 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. Our devices have a novel resistor inserted in their base bias current pass, which is designed to short-circuits DC components of the base current and conducts only envelope frequency signals. The impurity concentration at their emitter-base junctions is reduced by the effect of C doping suppressing B diffusion, and the emitter capacitance is decreased to half that of conventional SiGe HBTs as the result. The combination of these two modifications has significantly reduced the adjacent channel power leakage ratio (ACPR), and the idle current, without degrading power-added-efficiency (PAE). An optimized device with a total emitter area of 3390 μm~2 exhibited 48% PAE and 27.4-dBm output power with an ACPR of less than -40 dBc at an idle current of 20 mA under WCDMA modulation at 1.95 GHz and 3.4-V bias voltage.