Frequency-scalable SiGe bipolar RF front-end design

The optimum collector current density, at the global minimum noise figure (NF) point for a bipolar transistor, scales linearly with frequency, The optimum source impedance, on the other hand, remains constant if the device area is scaled inversely with frequency, As a result, transforming the design from one frequency to another can be achieved by simple circuit scaling Taking advantage of the shallow nature of the NF,;, global minima, it is possible to increase the linearity of the low-noise amplifier (LNA) or decrease its power consumption, which is required for multimode designs,with little degradation in NF These theoretical results have been applied to LNA and active mixer designs, and verified by constructing a 1.8-GHz frequency-scaled SiGe bipolar test chip, The measured LNA NF is 1.3 dB at 4.5 mA, while the double-balanced mixer achieves a single-sideband (SSB) NF of 6.1 dB for the low-linearity mode and an IIP3 and an SSB NF of +3 dBm and 6.6 dB, respectively for the high-linearity mode.