Degradation monitor

The degradation monitor is a code model with 4 inputs, to be paralleled to
a MOS transistor, for monitoring (reading and integrating) the
stress voltages on the device.

To start a degradation sim, put flag 'de' to ngbehavior, e.g. as
set ngbehavior=hsdea
in .spiceinit.

Degradation model parameters have to be provided, as shown in the example
file ngspice-master/examples/degradation/aging_par_ng.scs, starting with

.agemodel devmodel=sg13_lv_nmos simmodel=HCI1
+VGS0=0
+ <other parameters>

A code model monitor like
adegmon1 %v([z a vss vss]) mon degmon1
.model degmon1 degmon (tfuture=315336e4 l=0.15e-6 devmod="sg13_lv_nmos")
will automatically be added to each MOS device (here of type sg13_lv_nmos).
A .agemodel command with devmodel=sg13_lv_nmos is required (see aging_par_ng.scs).

The simulation model names by 'simmodel=HCI1' is coded into the above
cited code model monitor (see ngspice-master\src\xspice\icm\xtradev\degmonitor
with its 2 files cfunc.mod and ifspec.ifs.

The output is a list of the 3 degradation parameters provided by the HCI1 model.

Examples are provided in ngspice-master\examples\degradation