The bipolar junction transistor model in SPICE is an adaptation of the integral charge control model of Gummel and Poon. This modified Gummel-Poon model extends the original model to include several effects at high bias levels. The model automatically simplifies to the simpler Ebers-Moll model when certain parameters are not specified. The parameter names used in the modified Gummel-Poon 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 B-E junction, CJC, VJC, and MJC for the B-C junction and CJS, VJS, and MJS for the C-S (Collector-Substrate) junction.

The temperature dependence of the saturation current, IS, is determined by the energy-gap, 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 Gummel-Poon model are listed below. The parameter names used in earlier versions of SPICE2 are still accepted.

.MODEL <model name> NPN [model parameters]
.MODEL <model name> PNP [model parameters]

Modified Gummel-Poon BJT Parameters

Parameter Description Default Units Area
IS Transport saturation current 10-16 A *
BF Ideal maximum forward beta 100    
NF Forward current emission coefficient 1.0    
VAF Forward Early voltage V  
IKF Corner for forward beta high current roll-off A *
ISE B-E leakage saturation current 0 A *
NE B-E leakage emission coefficient 1.5    
BR Ideal maximum reverse beta 1    
NR Reverse current emission coefficient 1    
VAR Reverse Early voltage V  
IKR Corner for reverse beta high current roll-off A *
ISC B-C leakage saturation current 0 A *
NC B-C leakage emission coefficient 2    
RB Zero bias base resistance 0 Ω *
IRB Current where base resistance falls halfway to its min value A *
RBM Minimum base resistance at high currents RB Ω *
RE Emitter resistance 0 Ω *
RC Collector resistance 0 Ω *
CJE B-E zero-bias depletion capacitance 0 F *
VJE B-E built-in potential 0.75 V  
MJE B-E junction exponential factor 0.33    
TF Ideal forward transit time 0 s  
XTF Coefficient for bias dependence of TF 0    
VTF Voltage describing VBC dependence of TF V  
ITF High-current parameter for effect on TF A 0 A *
PTF Excess phase at freq=1.0/(TF*2PI) Hz 0 deg  
CJC B-C zero-bias depletion capacitance 0 F *
VJC B-C built-in potential 0.75 V  
MJC B-C junction exponential factor 0.33     
XCJC Fraction of B-C depletion capacitance connected to internal base node 1    
TR Ideal reverse transit time 0 s  
CJS Zero-bias collector-substrate capacitance 0 F *
VJS Substrate junction built-in potential 0.75 V  
MJS Substrate junction exponential factor 0    
XTB Forward and reverse beta temperature exponent 0    
EG Energy gap for temperature effect on IS 1.11 eV  
XTI Temperature exponent for effect on IS 3    
KF Flicker-noise coefficient 0    
AF Flicker-noise exponent 1    
FC Coefficient for forward-bias depletion capacitance formula 0.5    
TNOM Temperature at which the model parameters were measured. If this value is specified overrides the nominal TNOM value which is set in the options.   °C  
TABS Specifies the temperature at which the component operates. This value, if specified, takes precedence over the analysis temperature.    °C  
TREL Device temperature relative to current temperature. If this parameter is specified but not the parameter TABS then the current temperature of the component is equal to the current temperature plus TREL.    °C  



See also