Applying f/sub max/, f/sub t/, and f/sub mag/ 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)