Gnucap 0.31 release notes  (03/25/2002)

The most significant changes are the BJT model and "binning".


New features:

1. BJT model.

2. "Binning" for all MOS models.

3. Internal element: non-quasi-static poly-capacitor. (needed by BJT).

4. Enhancements to the data structures and model compiler to support
binning in general.

5. A line prefixed by "*>" is not ignored, in spite of the fact that
"*" usually begins a comment.  This is a deliberate incompatibility
with Spice.  If you prefix a line by "*>" it will be interpreted as a
non-comment in Gnucap, but a comment in Spice.

6. Circuit line prefixes of ">" and command prefixes of "-->" are
ignored.  This is so you can copy and paste whole lines, without
having to manually remove the prompt string.


Changes that may or may not be improvements.

1. It is not the default to include stray resistance in device models.
The option "norstray" will revert to the old behavior.  This is only a
change to the default value of "rstray".


Significant internal changes:

1. The internal element non-quasi-static poly-capacitor actually
works.  It is used by the BJT model, and will eventually be used by
MOSFET models.

2. There are now two poly_g devices: "CPOLY_G" and "FPOLY_G".  There
are interface differences that impact modeling.  Previously, there was
only one, which is equivalent to the "FPOLY_G".


Some things that are still partially implemented:

1. BSIM models, charge effects, "alpha0" parameter.  (computed then
ignored)

2. Configure still doesn't handle everything.

3. The model compiler still requires too much raw coding.


General comments:

The new BJT model seems to pass the CircuitSim90 test cases as well as
anything else, except where a missing feature prevented it from
working.  A few files would not run because of named nodes.  One file
(ring11) failed completely.  This file also has MOSFETs, with level 2
models.  The MOS level 2 model is not as robust as the BJT.  I believe
the problem is due to the voltage sync bug that still impacts the MOS
model.

Most of the models have has a reasonable amount of testing in DC, but
inadequate testing in AC and transient.  The BJT model has had more
testing than the others in AC and transient.  All differences
(relative to other simulators) that were observed can be attributed to
differences in transient step size control or tolerance checking.


Bugs (nothing new, but needs repeating):

1. The transmission line initial conditions are not propagated until
the transient analysis runs.


Bugs (newly discovered, not fixed):

1. In some cases, it is possible for the voltages at various stages of
model evaluation to get out of sync with each other.  In particular,
when device limiting occurs, the conversion from FPOLY to CPOLY form
may use the unlimited voltages, resulting in an erroneous conversion.
This problem has been fixed (before release) in the DC BJT model.  The
charge portion of the BJT model may still have the problem, but the
symptom rarely shows.  The MOS model is known to still have the
problem.  The symptom of the problem is occasional slow convergence or
non convergence.  There can be a single incorrect iteration that
throws the solution far from the intended path, then it usually
recovers eventually.  The fix is known, but I wanted to get the BJT
model out, so this fix will wait for the next release.

2. The "modify" command with multiple arguments seems to take only the
first one.  It used to work, but is broken in this release.  I am not
sure when it broke.


Hot items for a future release (no promises, but highly probable):

1. Charge effects and substrate current (alpha0) in BSIM models.  They
are computed, but not loaded to the matrix.  It was deferred waiting
for the poly-cap, but now that the poly-cap works, this missing part
of the MOS models should be working soon.

2. JFET model.

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. Spice-3 compatible "B" device.


To reach me, try this email address:
	aldavis@ieee.org

ftp sites:
	ftp://ftp.gnu.org/gnu/gnucap/gnucap-0.31.tar.gz
	ftp://ftp.geda.seul.org/pub/geda/dist/gnucap-0.31.tar.gz
	http://www.geda.seul.org/dist/gnucap-0.31.tar.gz
	ftp://sunsite.unc.edu/pub/Linux/apps/circuits/gnucap-0.31.tar.gz
