BJT Models (NPN/PNP)

<< Click to Display Table of Contents >>

Navigation:  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 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.

name

parameter

units

default

example

area

IS

transport saturation current

A

1.0e-16

1.0e-15

*

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 roll-off

A

infinite

200

*

ISE

B-E leakage saturation current

A

0

0.01

*

NE

B-E leakage emission coefficient

-

1.5

1.0e-13

 

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 roll-off

A

infinite

2000.01

*

ISC

leakage saturation current

A

0

0.01.0e-13

*

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

B-E zero-bias depletion capacitance

F

0

2pF

*

VJE

B-E built-in potential

V

0.75

0.6

 

MJE

B-E 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

high-current parameter for effect on TF

A

0

 

*

PTF

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

deg

0

 

 

CJC

B-C zero-bias depletion capacitance

F

0

2pF

*

VJC

B-C built-in potential

V

0.75

0.5

 

MJC

B-C junction exponential factor

-

0.33

0.5

 

XCJC

fraction of B-C depletion capacitance connected to internal base node

-

1

 

 

TR

ideal reverse transit time

sec

0

10ns

 

CJS

zero-bias collector-substrate capacitance

F

0

2pF

*

VJS

ubstrate junction built-in 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

flicker-noise coefficient

-

0

 

 

AF

flicker-noise exponent

-

1

 

 

FC

coefficient for forward-bias depletion capacitance formula

-

-.5

 

 

TNOM

Parameter measurement temperature

ºC

27

50