A self-backgating GaAs MESFET model for low-frequency anomalies

A self-backgating GaAs MESFET model which can simulate low-frequency anomalies has been developed by including deep-level trap effects. These cause transconductance reduction due to electron emission from EL2 in the depletion width change at the edge of the Schottky gate junction and the output conductance to increase due to the time-dependent net negative charge concentration in the semi-insulating substrate as a result of self-backgating with the applied signal frequency. This model has been incorporated in PSPICE and includes a time-dependent I-V curve model, a capacitance model, an RC network describing the effective substrate-induced capacitance and resistance, and a switching resistance providing device symmetry. An analytical capacitance model describes the dependence of capacitance on V/sub gs/ and V/sub ds/ and includes the channel-substrate junction modulation by the self-backgating effect. A transit-time delay is also included in the transconductances, g/sub m/ and g/sub mbs/, for model accuracy and to describe the phase shift of S-parameters. Measured data correspond to simulations by this model of the low-frequency anomalous characteristics, voltage-dependent capacitances, and S-parameters of conventional GaAs MESFETs for linear and microwave circuit design.<
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