Enhancement of SiGe HBT Linearity Characteristics with Current Source Bias

Linearity characteristics in terms of two-tone third order intermodulation distortion (IMD3) for common-emitter (CE) SiGe heterojunction bipolar transistors (HBT) are investigated at high frequency (6 GHz) with impedance matched for maximum output power. An approach to enhancing the linearity of SiGe HBTs at their high input power levels through the use of current bias instead of voltage bias is presented for the first time. Both measurements and simulations show that SiGe HBT linearity under high input power level (severe gain compression) can be improved. The reasons responsible for the linearity enhancement are discussed.