Ng-spice-rework-14
============

This is a major release in terms of bug-fixes. Some enhancements
have been included: BSIM4 model and support for EKV model. The 
source code for the latter must be obtained from EKV web site
(see DEVICE for more info). To enable EKV support you have
to obtain the code first and then use the configure switch
"--enable-ekv". 

The spice code contains an option to debug frontend code, now
this is available in configure as "--enable-ftedebug".



Ng-spice-rework-13
============

This is a major release in terms of fixes and enhancements.
A garbage collector support has been added. If the configuration
script detects that you have installed GC (Bohem-Weiser conservative 
garbage collector), it will use it. Some memory leaks have been 
fixed too.

Enhancements to the code comes from Alan's contribute code, a 
description of improvements follows (extracted form Alan's mail):

Output File Format Changes -

  Rawfile format changed to PSPICE Probe format (Usable with
  Demo version of Microsim's Probe).
  
  (NOTE: Do not rely on this, we may revert to the old format 
   in the next release). 

  Text mode .OP results even though "rawfile" written.

  Internal device nodes are not saved to "rawfile" (reduces
  file size). Optionally, these internal nodes can be replaced
  by device currents and saved.


DC Convergence Enhancements -

  "Source-Stepping" algorithm modified with a "Dynamic" step size.
  After each successful step, the node voltages are saved, the
  source-factor is increased by the step-factor, and the step-factor
  is increased (for the next step). If the step fails, i.e. the
  circuit does not converge, the source-factor is set to the value
  from the previous successful step, the previously stored node
  voltages are restored, the step-factor is reduced, the source
  factor is increased by this smaller step-factor, and convergance
  is attempted again.

  Same thing done for "Gmin-stepping" algorithm.

  "Gshunt" option added. This sets the "diagGmin" variable used in
  the gmin-stepping algorithm to a non-zero value for the final
  solution. (Normally this is set to zero for the final solution).
  This helps for circuits with floating nodes (and for some others
  too).

  The Gmin implementation across the substrate diodes of MOS1, MOS2,
  MOS3, MOS6 and BSIM3 devices, and across BJT base-emitter and
  base-collector diodes, was incorrect. Correcting this dramatically
  improved DC convergance. (I think this also effects BSIM1 and 2
  but I haven't fixed them yet !)

  The gm, gmb and gds calculations in the MOS3 model were all wrong.
  The device equations were fixed, leading to much improved
  convergance.

  The Vcrit value used for diode voltage limiting was calculated
  without taking into account the device area (and in some cases
  without using the temperature corrected saturation current).
  This could cause floating point overflows, especially in device
  models designed to be scaled by a small area, e.g. 2u by 2u diodes
  (area=4e-12). This is now fixed for Diode, BJT, MOS1, MOS2, and
  MOS3 models.

  The diode voltage limiting was modified to add negative voltage
  limiting. Negative diode voltages are now limited to 3*Vdp-10,
  where Vdp is the voltage from the previous iteration. If Vdp is
  positive, then the voltage is limited to -10V. This prevents some
  more floating point overflows. (Actually, I'm still playing with
  the best values for this).

  The Spice3 "fix" for the MOS3 gds discontinuity between the
  linear and saturated regions only works if the VMAX parameter
  is non-zero. A "tweak" has been added for the VMAX=0 case.


Transient Convergance Enhancements -

  Temperature correction of various diode capacitances was implemented
  slightly incorrectly, leading to capacitance discontinuities in
  simulations at temperatures other than nominal. This affected the
  Diode and MOS3 models.

  A mistake in the implementation of the MOS3 source-bulk capacitance
  model resulted in a charge storage discontinuity. This has been fixed.

  The level 2 MOSFET model seems to calculate Von and Vth values for
  the threshold and subthreshold values respectively, but then uses
  Vbin to calculate the Vdsat voltage used to find the drain current.
  However, a jump statement uses Von to decide that the device is in
  the "cutoff" region, which means that when this jump allows the
  drain current to be calculated, Vdsat can already be well above
  zero. This leads to a discontinuity of drain current with respect
  to gate voltage. The code is now modified to use Vbin for the jump
  decision. It looks like the code should actually use Vth as the
  threshold voltage, but since PSPICE and HSPICE both follow the
  original Berkeley code, this was left alone.


New Model Parameters -

  A PSPICE/HSPICE-like "M" device parameter (i.e. M devices in
  parallel) was added to the MOS1,2,3 and BSIM3 mosfet models.

  
Input Read-in and Checking -

  Numbers beginning with a + sign got the input routine confused.
  Fixed now.

  Attempts to nodeset (or .IC) non-existant nodes are flagged with a
  warning.

  PWL statements on Voltage or Current sources are now checked for
  "non-increasing" time-points at the start of the simulation.
  Previously each time-point was checked as it was reached during
  the simulation, which could be very annoying if you made a mistake
  which caused the simulation to fail after hours of run-time.
  
  A check which was performed at the end of each sub-circuit expansion
  was moved to the top level. This check makes sure that all sub-circuits
  have been defined, but in its original position, it meant that if a
  sub-circuit included ANY .MODEL statements at all, then ALL the models
  called in that sub-circuit must also be defined within that
  sub-circuit. Now SPICE behaves as expected, i.e. a subcircuit may
  define its own models, but may also use models defined at any level
  above.


Miscellaneous Fixes/Enhancements -

  MOS devices reported only half of the Meyer capacitances, and did not
  include overlap capacitances, when reporting to the .OP printout, or
  when storing device capacitances to the "rawfile".

  The ideal switch devices had no time-step control to stop their
  controlling voltages/currents overshooting the switching thresholds.
  The time-step control has been modified to use the last two time
  points to estimate if the next one will move the controlling
  voltage/current past a switching threshold. If this looks likely,
  then the time-step is reduced.

  The "rawfile" writing routines have been modified to print the
  "reference value" to the console during the simulation. This lets
  the user see exactly how far and how fast the simulation is
  proceeding. 

  .OP printout tidied up a lot to make the printout clearer.

  Analysis order changed to fix a "feature" where, if you ask for
  a .OP and a .TRAN in the same simulation, the node voltages
  printed out correspond to the .OP, but the device data was from
  the last timepoint of the .TRAN


Etc. -

  There are other minor bug fixes, and changes to reduce compiler
  warnings. There are probably some more significant fixes which
  I've forgotten :-)


Ng-spice-rework-12
============
Arno did a great work this summer!
The pole-zero analysis has been corrected. The error was introduced 
in an attempt to eliminate compiler warnings. The source has been 
reworked and info file have been updated. As you may see, a new dir 
called "spicelib" has been created, another step toward the separation
of the simulator from the frontend. 

Ng-spice-rework-11
============

Resistor code (device) has been modified to conform to spice3 device 
coding standard. 
A new step function (U2) has been introduced.
Documentation updated.

Ng-spice-rework-10
============

Added BSIM4 model and closed a couple of serious bugs. Added DEVICES
file to distribution. This file contains the status of device models
in this simulator. Read it, this file can save you a lot of time.

Ng-spice-rework-9
============

Thanks to Arno Peters now all device models are dynamically loaed on
demand.  Thay are linked as shared libraries. The next step is the
dlopen() one which will make possible to link devices without any
recompilation.



Ng-spice-rework-8
============

Applied Arno's patch.

From his mail message:

Hi Paolo,

I have prepared a source cleaning patch.

Features:

  + patches don't get polluted with differences between automatically
  generated Makefile.am files.  Usually these make up the biggest part
  of the patches.  This allows me to read the patch on the mailing
  list instead of sifting through 90% redundant and irrelevant changes.

  + the shell script autogen.sh automatically regenerates the required
  files if the user has automake, autoconf and libtool installed.

  + this feature is only valuable to developers, not to end users.


Usage of this patch, once incorporated:

  # create a working tree to work from
  cp -a ng-spice-rework-x ng-spice
  
  [ Changes made to ng-spice ]

  # clean up all the automatically generated files
  cd ng-spice; make maintainer-clean

  # extract the differences
  diff -ruN ng-spice-rework-x ng-spice > my.patch

  [ Patch sent to ng-spice mailing list or you ]

  # incorporate changes into the tree
  cd ng-spice-rework-x; patch -p1 < my.patch

  # update the automatically generated files
  cd ng-spice-rework-x; sh autogen.sh




Ng-spice-rework-7 (22 Mar 2000)
============

Bug fix release



Ng-spice-rework-6 (29 Jan 2000)
============

This porting includes:

1) BSIM3V3.1 model as level 49. This is the version modified by Serban
Popescu which understands the M parameter and implements HDIF.

2) BSIM3V3.2 model al Level 50. This is the standard Berkeley version.

3) Now the resistor model can accepts two differents values for DC and
AC resistance.



Ng-spice-rework-5 and 5_2  (Jan 2000)
============

Internal development release, buggy and not working. 

Ng-spice-rework-4  (22/12/99)
============

This porting includes a new feature:

1) dynamically loading of some device code as an experimental feature
for the future GPL simulator. Thanks to Arno Peters and Manu Rouat.

2) Patched the following bug (thanks to Andrew Tuckey for having
supplied the patch).
   
    * Wsw (current controlled switch) in subckt, parsing bug.
    * scale factor in arbitrary source.
    * bug in noise analisys.
    * save segmentation faults.
    
    
