VBIC Version 1.2 Released in SmartSpice and
UTMOST III
Introduction
The latest VBIC bipolar model v1.2 of Sep 24 1999 has been integrated into
SmartSpice and UTMOST III. It can be invoked
by specifying the model selector LEVEL=5 and the version selector VERSION=1.2.
in the .MODEL card. This new version becomes the default VBIC model.
A new model parameter REVISION has been introduced to invoke future updates
or older VBIC models. In SmartSpice/UTMOST III, only the old
version 1.1.5 is still supported and can be invoked by specifying VERSION=1.1
and REVISION=5. If other values are given, v1.2 is assumed. Aliases are
listed in Table 1.
VERSION (VERS)  Description  Units  Default 
VERSION (VERS)  Version parameter. Only 1.1 (if REV=5) and 1.2 (if REV= 0) are permitted, otherwise 1.2 is assumed.  

REVISION (REV, VREV)  Revision parameter. Only 0 (if VERS=1.2) and 5 (if VERS=1.1) are permitted, otherwise 0 is assumed.  

Table 1.
The explicit specification of VERSION and REVISION is strongly recommended
to avoid incompatibility problems between v1.1.5 and v1.2.
New Features in VBIC v1.2
Here is a summary list of major updates and enhancements announced in
v1.2 and relative to v1.1.5:
 temperature dependence of IKF
 separate temperature coefficients for intrinsic and extrinsic resistances RCX, RBX and RBP
 simple exponential baseemitter breakdown model
 reachthrough model to limit basecollector depletion capacitances
 separate activation energy for ISP
 selector available to switch to SGP qb formulation
 highcurrent rolloff coefficient
 fixed collectorsubstrate capacitance
 separate IS allowed for reverse operation in HBTs
 error fixed in the builtin potential temperature mapping (psibi function)
All these new features have been implemented in SmartSpice.
Only the 3terminal version of the model described in the official release
is not currently supported. Due to some of these changes, VBICv1.2 is
not fully backward compatible WIDTH the previous version (1.1.5).
New Model Parameters in VBICv1.2
All parameters supported in v1.1.5 are still used in v1.2. However, the
definition has slightly changed for the following ones:
Due to the separation of the temperature dependence for intrinsic and
extrinsic resistances, XRC and XRB now correspond to XRCI and XRBI, respectively.
Aliases XRCI and XRBI have been added for convenience. Due to changes
in the formulation of the single piece depletion capacitance model, the
smoothing factors AJE, AJC, AJS are now expressed in volts.
VBICv1.2 has 19 new model parameters that are shown in Table 2.
Parameter (alias)  Description  Units  Default 
XRBX  Temperature exponent of extrinsic resistance RBX  

XRCX  Temperature exponent of extrinsic resistance RCX  

XRBP  Temperature exponent of extrinsic resistance RBP  

XIKF  Temperature exponent of IKF  

ISRR  Reverse saturation current factor (HBTs)  

XISR  Temperature exponent of ISRR (HBTs)  

DEAR  Activation energy shift for ISRR (HBTs)  

EAP  Activation energy for ISP  

VBBE  BaseEmitter breakdown voltage, zero means infinity  

TVBBE1  First temperature coefficient of VBBE  

TVBBE2  Second temperature coefficient of VBBE  

NBBE  BaseEmitter breakdown emission coefficient  

TNBBE  Temperature coefficient of NBBE  

IBBE  BaseEmitter breakdown current  

QBM  Selector for SGP qb formulation  

NKF  High current rolloff coefficient  

VRT  BC reachthrough limiting voltage (0 means infinity)  

ART  BC reachthrough limiting smoothing factor  

CCSO  Fixed collectorsubstrate capacitance  

Table 2.
New Temperature Mappings
The following abbreviations are defined for convenience:
where TNOM is the temperature at which model parameter extraction
has been done. Td corresponds to the dynamic temperature if selfheating
is turned on or to the operating temperature otherwise.
 A bug in psibi mapping with temperature has been fixed. The psibi function is used to calculate builtin potentials PE, PC and PS at the device temperature as a function of related model parameters and activation energies EAIE, EAIC and EAIS, respectively. The updated expressions are (actually, only the expression pssio has been corrected):
 Some equations have been updated according to new model parameters:
 New equations have been added:
New Current Equations
 The equation of the ideal reverse current has been modified to account for a separate saturation current IS in reverse operation (HBTs). However backward compatibility is maintained if new model parameters ISSR, XISR and DEAR are unspecified (default values lead to). The new equation is:
 Two expressions for the base charge equation are now available and can be selected using the model parameter QBM. The standard GummelPoon formulation has been introduced. The highcurrent rolloff coefficient NKF is also supported. If NKF is unspecified, its default value is equal to 0.5 and the first expression reduces to for backward compatibility with v1.1.5.
 If VBBE > 0.0, a new contribution is added to intrinsic and extrinsic baseemitter currents Ibe and Ibex to account for the BE breakdown effect:
New Charge Equations
 A new depletion capacitance model with optional reachthrough limiting has been introduced to evaluate normalized depletion charges qdbc and qdbep (other depletion charges are still evaluated using the function qj). Assuming that V is the junction applied voltage, P is the junction builtin potential, FC is the forward bias depletion capacitance limit, M is the junction grading coefficient and AJ is the smoothing factor, the new function qjrt is defined by:
It is important to notice that qj and qjrt functions are identical if VRT is set to zero (no reach through limiting). The influence of the reachthrough limiting on normalized depletion capacitances only occurs for reverse biased junction as shown on Figure 1 and Figure 2. Figure 1 corresponds to the SGPlike model, where the depletion capacitance linearly increases for values of forward bias greater than FC.P. Figure 2 corresponds to the single piece model where the depletion capacitance smootly limits to its value at FC.P. The effect of reachthrough limiting is similar for both models.
Figure 1.  Figure 2. 
Another important point is that the qj function implemented in v1.1.5 has been slightly modified in v1.2. The smoothing factor AJ has been replaced by 4*AJ*AJ in vl and vl0 expressions.
 The contribution of the fixed capacitance CCSO has been added to the basecollector charge Qbcp of the parasitic device. The new equation is: