<< Click to Display Table of Contents >> Navigation: AutoTRAX PCB Design Express (DEX) > Designs > Circuit Simulation > The Spice Reference Manual > Circuit Description > Circuit Elements and Models > Transistors and Diodes > BJT Models (NPN/PNP) 
The bipolar junction transistor model in SPICE is an adaptation of the integral charge control model of Gummel and Poon. This modified GummelPoon model extends the original model to include several effects at high bias levels. The model automatically simplifies to the simpler EbersMoll model when certain parameters are not specified. The parameter names used in the modified GummelPoon model have been chosen to be more easily understood by the program user, and to reflect better both physical and circuit design thinking.
The dc model is defined by the parameters IS, BF, NF, ISE, IKF, and NE which determine the forward current gain characteristics, IS, BR, NR, ISC, IKR, and NC which determine the reverse current gain characteristics, and VAF and VAR which determine the output conductance for forward and reverse regions. Three ohmic resistances RB, RC, and RE are included, where RB can be high current dependent. Base charge storage is modeled by forward and reverse transit times, TF and TR, the forward transit time TF being bias dependent if desired, and nonlinear depletion layer capacitances which are determined by CJE, VJE, and MJE for the BE junction , CJC, VJC, and MJC for the BC junction and CJS, VJS, and MJS for the CS (CollectorSubstrate) junction. The temperature dependence of the saturation current, IS, is determined by the energygap, EG, and the saturation current temperature exponent, XTI. Additionally base current temperature dependence is modeled by the beta temperature exponent XTB in the new model. The values specified are assumed to have been measured at the temperature TNOM, which can be specified on the .OPTIONS control line or overridden by a specification on the .MODEL line.
The BJT parameters used in the modified GummelPoon model are listed below. The parameter names used in earlier versions of SPICE2 are still accepted.
name 
parameter 
units 
default 
example 
area 
IS 
transport saturation current 
A 
1.0e16 
1.0e15 
* 
BF 
ideal maximum forward beta 
 
100 
100 

NF 
forward current emission coefficient 
 
1.0 
1 

VAF 
forward Early voltage 
V 
infinite 
1 

IKF 
corner for forward beta high current rolloff 
A 
infinite 
200 
* 
ISE 
BE leakage saturation current 
A 
0 
0.01 
* 
NE 
BE leakage emission coefficient 
 
1.5 
1.0e13 

BR 
ideal maximum reverse beta 
 
1 
2 

NR 
reverse current emission coefficient 
 
1 
0.11 

VAR 
reverse Early voltage 
V 
infinite 
1200 

IKR 
corner for reverse beta high current rolloff 
A 
infinite 
2000.01 
* 
ISC 
leakage saturation current 
A 
0 
0.01.0e13 
* 
NC 
leakage emission coefficient 
 
2 
1.5 

RB 
zero bias base resistance 
Ohm 
0 
100 
* 
IRB 
current where base resistance falls halfway to its min value 
A 
infinite 
0.1 
* 
RBM 
minimum base resistance at high currents 
Ohm 
RB 
10 
* 
RE 
emitter resistance 
Ohm 
0 
1 
* 
RC 
collector resistance 
Ohm 
0 
10 
* 
CJE 
BE zerobias depletion capacitance 
F 
0 
2pF 
* 
VJE 
BE builtin potential 
V 
0.75 
0.6 

MJE 
BE junction exponential factor 
 
0.33 
0.33 

TF 
ideal forward transit time 
sec 
0 
0.1ns 

XTF 
coefficient for bias dependence of TF 
 
0 


VTF 
voltage describing VBC dependence of TF 
V 
infinite 


ITF 
highcurrent parameter for effect on TF 
A 
0 

* 
PTF 
excess phase at freq=1.0/(TF*2PI) Hz 
deg 
0 


CJC 
BC zerobias depletion capacitance 
F 
0 
2pF 
* 
VJC 
BC builtin potential 
V 
0.75 
0.5 

MJC 
BC junction exponential factor 
 
0.33 
0.5 

XCJC 
fraction of BC depletion capacitance connected to internal base node 
 
1 


TR 
ideal reverse transit time 
sec 
0 
10ns 

CJS 
zerobias collectorsubstrate capacitance 
F 
0 
2pF 
* 
VJS 
ubstrate junction builtin potential 
V 
0.75 


MJS 
substrate junction exponential factor 
 
0 
0.5 

XTB 
forward and reverse beta temperature exponent 
 
0 


EG 
energy gap for temperature 
eV 
1.11 


XTI 
temperature exponent for effect on IS 
 
3 


KF 
flickernoise coefficient 
 
0 


AF 
flickernoise exponent 
 
1 


FC 
coefficient for forwardbias depletion capacitance formula 
 
.5 


TNOM 
Parameter measurement temperature 
ºC 
27 
50 
