Robust stability of FET circuits at high frequency

A necessary and sufficient condition for robust stability of a group of electronic circuits at high frequency that contain of source-coupled pairs is proposed. When a source-coupled pair is used as a single input-output unit, it has uncertainty in its transfer function at high frequencies. This uncertainty can cause instability in closed-loop electronic circuits and is modelled as multiplicative perturbation in the transfer function of the source-coupled pair. Based on this uncertainty model, a necessary and sufficient condition for robust stability in these electronic circuits is presented. This condition guarantees internal stability of these electronic circuits at this frequency.