AC SIDEGATING IN GAAS-MESFETS

The bias and frequency dependence of a.c. sidegating in GaAs MESFETs was modeled using a distributed R-C network. The resultant analytic expression for the sidegate transconductance was compared with experimental results over the range of 100 Hz-100 kHz. They agreed in that the sidegating at small drain-source voltage exhibits a maximum as a function of gate bias, while at large drain-source voltage the sidegating increases and eventually saturates with gate voltage, and is not sensitive to drain-source voltage. The present experimental measurements show that a.c. sidegating (like d.c.) is greatly enhanced after a negatively-biased sidegate reaches a threshold. Both experimental data and the model show that a.c. sidegating increases approximately as w1/2 at high frequencies.