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ACS 0.29 release notes (06/30/2001)
The primary effort has been to implement IBIS, which is still not
done. The changes here are mostly infrastructure changes needed to
support IBIS.
New features:
1. "Fit" function has choice of fit order and extrapolation. You can
have order 0, 1, 2, or 3.
2. "Posy" has even and odd options, to determine what happens in the
negative region.
3. Modelgen improvements. It now is useful for the whole device,
sometimes. It now handles probes and the device side of the model.
The diode uses it completely. There are still a few missing features
needed for the MOSFET and BJT.
4. Spice-3 compatible semiconductor resistor and capacitor.
5. "Table" model statement.
Improvements, bug fixes, etc.
1. Option "numdgt" really works.
2. Better error messages from modelgen.
3. Code changes for optimization of commons. This should reduce
memory use, sometimes, by sharing commons. Common sharing is still
not fully implemented.
4. Fix two bugs that sometimes caused problems after a "modify" or on
a "fault".
5. Better handling of "vmin" and "vmax". It should be much less
likely that limiting causes convergence to a nonsense result.
Some things that are still partially implemented:
1. Internal element: non-quasi-static poly-capacitor.
2. BSIM models, charge effects, "alpha0" parameter. (computed then ignored)
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from the history file:
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New features:
1. New probes: diode G, mos IBD, IBS, GBD, GBS.
2. New options: "floor" and "vfloor". (Floor was in the manual, but
not in the simulator.)
Improvements, bug fixes, etc.
1. There is a change to the way behavioral modeling conditionals are
handled. It should now be 100% compatible with SPICE, considering the
subset that duplicates SPICE. There are still significant extensions
beyond SPICE, particularly that you can have behavioral resistors,
capacitors, inductors, etc.
2. Parameter default calculations are now done in a manner consistent
with Spice 3f5. Previously, it was supposedly consistent with Spice
2g6.
3. A bug in calculation of threshold voltage of the level 6 model, for
P channel devices, has been fixed.
4. A bug in calculation of Meyer capacitances when the device is
reversed has been fixed. This bug sometimes caused a discontinuity at
vds=0.
5. I have added some smoothing to the Meyer mos capacitor models.
This improves convergence. The down side is that sometimes the
answers are different. It is probably a little better, when
considering closeness to reality, but it is still Meyer's model.
6. MOSFET parasitic diodes are now the same as those used in Spice.
7. There are subtle changes in the diode model. I think this usually
improves convergence.
8. Charge calculation in Meyer capacitors and diode capacitiors is now
supposedly Spice 3 compatible.
9. An error in BSIM3 scaling has been fixed.
Some things that are still partially implemented:
1. Internal element: non-quasi-static poly-capacitor.
2. BSIM models, charge effects.
Bugs (nothing new, but needs repeating):
1. The transmission line initial conditions are not propagated until
the transient analysis runs.
2. The makefile does not set up the proper link for the model
compiler. You need to do it manually.
3. A bad setting of "vmax" and "vmin" can lead to convergence to a
nonsense result. It is not as bad now as it used to be.
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ACS 0.27 release notes (06/03/2000)
New features:
1. BSIM3 model, DC.
They work for AC and transient analysis, but only the DC effects
actually work. The next release should have the charge effects. For
now, it fakes it with Meyer's model.
2. A first cut at a model compiler, to aid in development of new
models. Models are described in a ".model" file, which is processed
to automatically generate the ".h" and ".cc" files. This version
fully handles the ".model" statement part of it, but leaves the device
and common sections the old way. Eventually, the entire process will
be automated. The old way still works.
3. "Fit" behavioral modeling function, which fits a curve to a set of
data. You can specify the order of the fit, which is piecewise
polynomials. For now, the order may be 1 (linear, like PWL) or 3
(cubic splines). You may also specify the boundary consitions.
4. More probes.
Some things that are partially implemented:
1. Internal element: non-quasi-static poly-capacitor. It is needed by
the BSIM3 and EKV models. Eventually, it will be available as a
netlist item, but not yet.
Bug fixes:
1. PWL could fail if there were duplicate points at the beginning. It
still does, but gives a reasonable error message.
2. Some "dot commands" were ignored if there were spaces before the
dot. This was particularly annoying if the line was supposed to be
".end" which should make it exit. It didn't, leaving it in
interactive mode, a major annoyance in a script.
Other improvements:
1. There is a change to the way integration in capacitors is done. It
is now strictly based on charge (i = dq/dt). The old version was
based on capacitance (i = C * dv/dt) which is strictly incorrect. The
dC/dt term was missing (i = C * dv/dt + v * dC/dt). This is a
non-issue when C is constant.
2. More documentation on internals.
Changes that I think are improvements, but some may disagree:
1. The command line is a little different. In the old version,
"acs file" would run it, and whether it exited or not depended on
whether there was an ".end" line. Now, by default, it just loads the
file in preparation for interactive use. If you want batch mode, say
"acs -b file".
2. The regression suite is included in the standard distribution.
Changes that are not really improvements:
1. Due to the model compiler, the build process is a little more
complicated. To do a complete build, you must build the model
compiler first, then the simulator. If you are not making any new
models, you can probably get away with just building the simulator.
This will change in a future release.
Bugs:
1. The transmission line initial conditions are not propagated until
the transient analysis runs.
2. The makefile does not set up the proper link for the model
compiler. You need to do it manually.
Hot items for a future release (no promises, but highly probable):
1. Charge effects in BSIM models. They are computed, but not loaded
to the matrix.
2. Completion of model compiler, and its documentation.
3. Completion of multi-rate.
4. Homotopy methods to improve convergence.
5. Transmission line accuracy and speed improvements, using a step
control mechanism similar to that used for capacitors.
6. Parameterized subcircuits and defined parameters.
7. A "trigger" element, so time dependent values can be triggered by
the circuit, as an alternate to simple time.
To reach me, try this email address:
aldavis@ieee.org
ACS ftp sites:
ftp://ftp.geda.seul.org/pub/geda/dist/acs-0.27.tar.gz
http://www.geda.seul.org/dist/acs-0.27.tar.gz
ftp://sunsite.unc.edu/pub/Linux/apps/circuits/acs-0.27.tar.gz
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New features:
1. BSIM1, BSIM2 models -- DC only.
2. New elements:
trans-capacitor
voltage controlled capacitor
voltage controlled conductance
voltage controlled resistor
3. Optional new syntax, with type first so component labels can start
with any letter, and the choice of components is no longer limited by
the 26 letters. This was necessary for a clean syntax
for #2.
4. Some new parameters on existing devices, also a side
effect of the BSIM work.
5. The manual in HTML form. The manual source is still in LaTeX,
which can be used to generate HTML, PDF, Postscript, or many other
formats.
Bug fixes:
1. An error causing truncation error to be underestimated has been fixed.
Other improvements:
1. MOSFET model evaluation is a little faster, due to use of one of
the new elements to replace several old ones. I have seen 40%, but
20% is more likely. The improvement is most evident on busy circuits,
where the ACS speed enhancements based on latency exploitation
contribute more overhead than their value, that is .. the type of
circuit that has run faster in Spice than ACS.
2. More documentation on internals.
Changes that I think are improvements, but some may disagree:
1. Truncation error based step control is disabled when Euler's method
is selected. The justification for this is that the reason for
selecting Euler's method is to avoid the artifacts of high order
methods on "stiff" poles. Without this change, a "stiff" pole would
cause an unreasonably small step size. This did not appear to be much
of a problem in the old release because the use of an incorrect
formula for estimating truncation error. A "stiff" pole is one that
has a response so fast it can be thought of as instantaneous.
2. The "help" command, with its 4 year old help file, has been
removed. The concept is really obsolete. With the HTML form of the
manual, a full online manual is a better replacement.
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ACS is a general purpose circuit simulator. It performs nonlinear
dc and transient analyses, fourier analysis, and ac analysis
linearized at an operating point. It is fully interactive and
command driven. It can also be run in batch mode or as a server.
The output is produced as it simulates. Spice compatible models
for the MOSFET (level 1,2,3,6) and diode are included in this
release.
Since it is fully interactive, it is possible to make changes and
re-simulate quickly. The interactive design makes it well suited
to the typical iterative design process used it optimizing a circuit
design. It is also well suited to undergraduate teaching where
Spice in batch mode can be quite intimidating. This version, while
still officially in beta test, should be stable enough for basic
undergraduate teaching and courses in MOS design, but not for
bipolar design.
In batch mode it is mostly Spice compatible, so it is often possible
to use the same file for both ACS and Spice.
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