Applying fmax, ft, and fmag for Microwave Transistor Designs at Microwave and Millimeter-Wave Frequencies [Application Notes]

Traditional descriptions of transistor power gains versus frequency lead to the conclusion that Mason's unilateral gain is unity at f_max and G_ma extrapolated to unity gives f_mag, where f_max > f_mag> (Vendelin et al., 1990). A similar figure of merit is derived from current gain (|h₂₁|²) extrapolated to unity, giving the f_t of the transistor. It should be recognized the f_max is invariant to the common lead, i.e., U_cs = U_cg = U_cd, but this is not true for G_ma. Trew and Steer (1986) pointed out the equivalence of F _max and f_mag based upon an equivalent circuit analysis for the common-source (CS) FET (field-effect transistor)