Unified analytical model of HEMTs for analogue and digital applications

A unified model for the I-V characteristics of HEMTs valid for the subthreshold, linear and saturation regions of operation is presented. There is a smooth transition in the current from subthreshold to above threshold and also from linear to saturation. This results in highly continuous channel conductance (g_ds) and transconductance (g_m), which are important circuit parameters in small signal analysis. Comparisons with experimental data show that the model is accurate and valid over a wide range. Further, it is established that the model holds good promise for analogue circuit design by subjecting it to a few benchmark tests. In addition, the model, which was originally developed for n-channel HEMTs, has been suitably modified to predict the I-V characteristics of p-channel HEMTs as well. Finally, an inverter circuit using p-channel HEMT as load and n-channel HEMT as driver has been successfully simulated using the circuit simulator SABER and the nature of the inverter characteristics are found to agree well with the experimental results.