That depends on the SPICE simulator. The syntax for
piecewise-linear transconductance elements differs
from one to another. Time-domain behavior is even
more interesting; basically, you have to take the
four V/T curves and back them through the V/I curves
to get turnon and turnoff profiles for the pullup
and pulldown devices, then make up a subcircuit
that modulates the transconductances to get the
same result.
-- D. C. Sessions [email protected]