Nonlinear distortion and mixing processes in field-effect transistors

From the transfer characteristic of the junction-type field effect transistor, nonlinear distortion effects can be evaluated without difficulty. It is shown how the conversion transconductance can be calculated as a function of the operating point, the local oscillator voltage and the oscillator output resistance. A new method has been derived which permits a very precise evaluation of the conversion transconductance even if the operating point is chosen in the cutoff region. The investigations deal with the influence of the signal amplitude upon nonlinear distortion in mixer stages and also treat the generation of whistles. The conversion transconductance exhibits a flat maximum as a function of the gate bias voltage. Thus, an optimum operating range can be indicated where the ratio between mixing current and distortion product currents is most favorable. Finally, it is shown how the operating point can be preserved in stabilized mixer stages and some reference details for the behavior of FET stages at very high frequencies are given.