Utilization and validation of HBT nonlinear frequency domain behavioral models in the design and simulation of oscillator circuits

Recently new behavioral model formulations, i.e. PHD model, X-parameters, have been shown to robustly describe the nonlinear behavior of transistors. Such models being obtained from measurements performed using the emerging family of nonlinear network analyzers. The critical next step is to further demonstrate the usefulness and validity of such models in CAD design. In this paper it will be shown that such models can be successfully utilized in the design and performance prediction of free running RF oscillators, when using an adequate extraction strategy. For that purpose, a PHD type behavioral model was extracted at two different output port impedances, from the measured response of a SiGe HBT stimulated by a set of harmonically related discrete tones. For that purpose, LSNA (Large Signal Network Analyzer) nonlinear measurements, at an adequate device load impedance, and different output active injections levels have been used. To check the model validity and efficiency, its performance has been studied and compared at device and oscillator circuit level. This analysis showed the importance of the election of an appropriate output impedance for the model generation. Using this model, HBT-based oscillators have been successfully designed and fabricated.