Minimization of intermodulation distortion in GaAs MESFET small-signal amplifiers

It is shown how the intermodulation (IM) distortion performance of a small-signal amplifier can be optimized when the amplifier is designed according to available-gain criteria. In this process the MESFET's output is conjugate-matched and its input is mismatched to obtain a specified gain. This method generally results in a better dynamic range than obtained with other options such as matching the input and mismatching the output or simultaneously matching both the input and output (which, in many cases, is impossible). In available-gain design the value of source impedance that provides the desired gain is not unique and can be selected to optimize IM levels. A numerical formulation of the Volterra series allows a complete equivalent circuit of the FET to be used, and the intermodulation calculations include all feedback effects. The sensitivity of the IM intercept point (IP/sub 3/) to the source-reflection coefficient, Gamma /sub s/, is shown to decrease with increasing frequency and is related to the MESFET's stability.<
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