Systematic analysis of RF distortion in SiGe HBT´s

A systematic analysis of the RF intermodulation in SiGe HBT´s is performed using a new Volterra series-based approach. The relative dominance of individual nonlinearities and their interaction were shown to vary with source/load, bias current, and CB feedback. The C/sub CB/ and avalanche multiplication nonlinearities are the dominant factors in determining the overall linearity, and are responsible for the load dependence. A cancellation mechanism between the avalanche current I/sub CB/ nonlinearity and the CB capacitance C/sub CB/ nonlinearity is identified. The current dependence of avalanche multiplication was shown to be beneficial to linearity. The results suggest that there is a fundamental limit to achieving high f/sub T/ and high linearity and multiple collector profiles need to be used for leverage in RF circuit design.