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 (|h 21 | 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)