🚀 go-pugleaf

One more bug discovered in SPICE 2g6.

Recently, we pointed out that Berkely's version of SPICE2g6 differs
from the U of Washington in calculating FACTOR. We agree with
the responses from Xerox and U of Waterloo that FACTOR should be calculated
as:
	FACTOR = 0.125D0*FNARROW*TWOPI*EPISSIL/(COX*XW)
		where FNARROW = DELTA is a dimensionless parameter

As a result SUXES (paramter extraction program from Stanford) should
also use the same equation to calculate FACTOR for consistency.

Further examination reveals that there is one more problem with the
calculation of VTH. Around line 2039 of the file "dctran2.f" (from U of W)
VTH is calculated as:

	CDONCO=-(GAMASD*DSRGDB+DGDDVB*SARG)+FACTOR
	XN=1.0D0+CFS/COX*XW*XL+CDONCO
        VON=VON+VT*XN

		where VON is VTH

We feel that in calculating XN, multipling XL and XW with CFS/COX is NOT
correct. Futhermore, tracing the dimension of the above lines shows an
inconsistency with the final dimension. XN should have been a dimensionless
value. From the defintion we observe that CFS = q*NFS, where
NFS according to SPICE manual has #/cm^2 as its dimension. This gives
CFS a dimension of q/cm^2. Therefore the dimension of CFS/COX is
Volt.

If we were to correct the calculation of FACTOR as suggested above,
we should also correct the XN calculation. We propose the following
changes to line 2039 and line 2040:

	XN=1.0D0+CDONCO
	VON=VON+VT*XN+CFS/COX

Again, SUXES should be changed to match these changes.

We invite others to comment on our suggestion.

Cheers,

Je-Hurn Shieh
Shih-Lien Lu
Ming Hsu

ARPA: sllu@mosis.edu