The well known definition for the current gain cut-off frequency
is given in (4.10).
This definition of
has various approximations in terms of intrinsic small-signal
equivalent elements. The most important approximations for a HEMT are (assuming the parasitic
inductances and capacitances to be stripped off) according to Baeyens in :
is defined in several manners depending on the invariants used for
its definition . Defining the Unilateral Power Gain allows for the highest values
in a device representing the maximum gain in a lossless reciprocal deembedding
The MSG drops with -10 dB/dec as a function of frequency. The transition between the two
for = 1 defines the frequency
, from which
based on MAG/MSG eventually can be
extrapolated with a slope of -20 dB/dec for a given gate width
. The frequency:
defines the stability point and is expressed as a function of small-signal elements . depends the single finger gate width and is a critical quantity for amplifier design, especially for mm-wave applications. It will be analyzed in Chapter 7 with respect to statistical changes of mm-wave devices.