Gate bias voltage dependence of Cardiff admittance model in Ka-band GaAs pHEMTs

This paper analyzes the dependence vs. gate bias voltage of the coefficients of the Cardiff model in the admittance form. The load-pull measurement data used to extract the model, inclusive of input power sweep, is taken on a GaAs pseudomorphic high electron mobility transistor (pHEMT) at the frequency of 36 G Hz. The gate bias is swept in class C and in class AB and a different set of coefficients is extracted at each bias point. It is observed that the model coefficients can be fitted vs. bias using a linear function within the class C and class AB ranges. This allows to predict the model coefficients within a range of bias voltages with load-pull measurements at only a few bias points, significantly reducing the measurement effort. Using the predicted coefficients, the model shows a global error lower than -31 dB for the DC and fundamental output current.