This paper describes an improved nonlinear GaAs FET model and its parameter extraction procedure for almost all operating conditions such as the small-signal condition, the power saturated condition, and the controlled-resistance condition. The model is capable of modeling the gate voltage dependent drain current and its derivatives in the saturated region as well as the drain voltage dependent drain current and its derivatives in the linear region. The model can take into account the frequency dispersion effects of both transconductance and output conductance. The model describes forward conduction and reverse conduction currents. Deriving the capacitance part of the model from unique charge equations satisfies charge conservation. The model accurately predicts voltage-dependent S-parameters, spurious response in an active condition and inter-modulation response in the controlled-resistance condition of a GaAs FET.

This paper proposes an improved nonlinear FET model along with its parameter extraction procedure suitable for the accurate prediction of inter-modulation product's levels (IM) and spurious responses in active and passive applications. This new model allows accurate capture of the drain current behavior and its derivatives with respect to the gate voltage and the drain voltage in the both the saturated and linear regions of the I-V biasing domain. It was found that this model accurately predicts the bias-dependent S-parameters as well as IM's levels for both amplifier and mixer applications up to mm-wave frequencies.

The effect of DC offset on multi-input multi-output (MIMO) direct transceivers with adaptive modulation (AM) is discussed in this paper. A variable-rate variable-power (VRVP) AM system with perfect channel state information (P-CSI) at both the transmitter and receiver in a MIMO scenario is considered. The DC offset is modeled as a zero mean complex Gaussian distributed random variable. By this modeling of the DC offset, the analytical expression for degraded bit error rate (BER) is derived. To derive this analytical expression, we establish a reasonable approximation. The good agreement between the analytical and simulation results shows that the approximation is valid and confirms the accuracy of the analytical expressions. Moreover, an approach to improve the degraded BER in these systems is introduced. For this purpose, we introduce a design for AM MIMO systems that takes account of DC offset and its effectiveness is confirmed. Throughput analysis for the AM MIMO system in the presence of DC offset is presented in this paper too. An analytical expression for throughput is derived and approximated to a simpler equation. At last, throughput results are compared to the simulation outcomes.