THE FET7 MOS Models in Analog
This release features a new family of MOS models, the FET7 series
(three-terminal gates PFET7T and NFET7T, and four-terminal gates
PFET7F and NFET7F) as well as several supporting gates. These models
are different from previous MOS models in analog, in structure as well
as form. This Web page is a quick introduction to these models; for
complete details, see this paper [Postscript,
300 KByte compressed] [Adobe PDF, 680 KByte,
requires Acroread 3.0].
The model on which these gates are based is parameterized in a new
way. The parameters are properties of the physical construction of
devices. In addition, they are independent properties. Therefore, it
makes sense to vary one parameter while the others are left fixed. This
is useful in terms of finding values which give a good fit to a given
process, and also as a way of exploring the effect of process values
on device and circuit behavior.
The simulator has been modified so that the simulation environment itself
about MOS physics and fabrication; in previous models, each gate held
this information redundantly. This information has been broken up into
- Temperature The THERMAL gate lets the user view and
change the ambient chip temperature. Temperature-dependent quantities
in the MOS modeling system are automatically updated to reflect
temperature changes.Unfortunately, the ambient temperature set by the
THERMAL gate is not presently used by gates outside the FET7 family,
such as the DIODE1 gate.
- Physical Constants The PHYSICAL gate holds fundamental
physical quantities, such as the Boltzmann constant, and derived
quantities from these constants, such as kT/q. Derived quantities are
denoted by the annotation (Computed) in the parameter description.
These derived quantities cannot be directly changed by the user, but
will automatically be updated if the user changes their underlying
- Fabrication Parameters The channel-specific fabrication
parameters for N- and P-channel devices, along with derived quantities
of interest, are displayed in the DEVTECHN and DEVTECHP gates. Several
channel-independent fabrication parameters are in the PHYSICAL gate.
- Run-Specific Parameters The parameters in the DEVTECHN and
DEVTECHP gates are relatively constant from run to run of a given
process. In contrast, a small number of channel-specific parameters
do vary significantly from run to run, and from transistor to
transistor. The gate RUNSPEC provides a way to change these parameters
for all transistors in the simulation; in addition, these parameters
can be varied on a per-transistor basis, to simulate various forms of
- Transistor-Specific Parameters The user can change the
geometry of each FET7 gate (drawn width and length in lambda, source
and drain area in square microns), and the offset parameters mentioned
above. Derived parameters (which may be voltage and temperature
dependent) are displayed for each transistor (Vt, kappa, Early voltage
and linear-lumped capacitances). These parameters cannot be directly
changed, but reflect changes in their underlying parameters and
voltages in real time.
At start-up, the simulator reads in the default parameters for
the FET7 series from the file log/lib/mos.cnf. The default mos.cnf
file contains parameter values suitable for the MOSIS SCN 1.2u
process (SCN12, fab run N52V);
this file also appears as mosscn12.cnf. Parameter files for the HP
CMOS26G 0.8um process (mos26g.cnf) and the HP CMOS14TB 0.5um process
(mos14tb.cnf) are also supplied.
The annotated file mos_example.cnf explains the process of
converting MOSIS-supplied documentation for a process to a cnf
file. We hope users will create cnf files for other processes, and
send them along to us for inclusion in later releases.
The LOGSPC utility for creating Spice files from Log
schematics has been updated to be FET7-aware. See the file
log/lib/spctest.lgf for an example of using FET7 transistors for
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