Three-region analytical models for MESFETs in low-voltage digital circuits

Analytical models for self-aligned gate, GaAs and Si MESFET/JFETs that predict static current-voltage characteristics continuously in three regions of operation (subthreshold, linear, and saturation,) are presented. The characteristic equations are closed-form and describe behavior explicitly in terms of terminal voltages. Comparisons of model predictions with measurements in all regions of device operation are presented. In addition to physical insight into MESFET/JFET operation, the models, due to their relative simplicity, promise digital circuit simulations with accuracy, ease, and efficiency. The models indicate that in typical DCFL (direct-coupled FET logic) circuits MESFETs with undoped substrates are superior to those on highly doped substrates with respect to noise margin considerations