The impact of low-frequency noise variations on the modeling and operation of SiGe circuits

The influence of geometrical-scaling-induced low-frequency noise (LFN) variations on SiGe HBT circuit operation is investigated for the first time. The circuit-level impact of these noise variations occurs not only at low frequencies but also at high frequencies via up-conversion through the device nonlinearities. This up-conversion process is illustrated using a LC VCO as a case study. Given the potential importance of the LFN variations on mixed-signal circuits, a robust model is desired to capture the random noise magnitude shift and frequency dependent sample-to-sample deviation from 1/f behavior that is the signature of this unique phenomenon. We present for the first time a statistical LFN model for SiGe HBTs which accurately models the characteristics of this scaling-induced LFN variation. This model can also be easily implemented in BSIM models for deep-sub micron CMOS.