Bipolar Junction Transistor (BJT) Model
Model Kind
Transistor
Model Sub-Kind
BJT
SPICE Prefix
Q
SPICE Netlist Template Format
@DESIGNATOR %1 %2 %3 @MODEL &"AREA FACTOR" &"STARTING CONDITION" ?"INITIAL B-E VOLTAGE"|IC=@"INITIAL B-E VOLTAGE", @"INITIAL C-E VOLTAGE"| ?TEMPERATURE|TEMP=@TEMPERATURE|
Parameters (definable at component level)
The following component-level parameters are definable for this model type and are listed on the Parameters tab of the Sim Model dialog. To access this dialog, simply double-click on the entry for the simulation model link in the Models region of the Component Properties dialog.
| Area Factor | specifies the number of equivalent parallel devices of the specified model. This setting affects a number of parameters in the model. |
| Starting Condition | set to OFF to set terminal voltages to zero during operating point analysis. Can be useful as an aid in convergence. |
| Initial B-E Voltage | time-zero voltage across base-emitter terminals (in Volts). |
| Initial C-E Voltage | time-zero voltage across collector-emitter terminals (in Volts). |
| Temperature | temperature at which the device is to operate (in Degrees Celsius). If no value is specified, the default value assigned to TEMP on the SPICE Options page of the Analyses Setup dialog will be used (Default = 27). |
Parameters (definable within model file)
The following is a list of parameters that can be stored in the associated model file:
| IS | transport saturation current (in Amps). (Default = 1.0e-16). |
| BF | ideal maximum forward beta (Default = 100). |
| NF | forward current emission coefficient (Default = 1). |
| VAF | forward Early voltage (in Volts). (Default = infinite). |
| IKF | corner for forward beta high current roll-off (in Amps). (Default = infinite). |
| ISE | B-E leakage saturation current (in Amps). (Default = 0). |
| NE | B-E leakage emission coefficient (Default = 1.5). |
| BR | ideal maximum reverse beta (Default = 1). |
| NR | reverse current emission coefficient (Default = 1). |
| | reverse Early voltage (in Volts). (Default = infinite). |
| IKR | corner for reverse beta high current roll-off (in Amps). (Default = infinite). |
| ISC | B-C leakage saturation current (in Amps). (Default = 0). |
| NC | B-C leakage emission coefficient (Default = 2). |
| RB | zero bias base resistance (in Ohms). (Default = 0). |
| IRB | current where base resistance falls halfway to it minimum value (in Amps). (Default = infinite). |
| RBM | minimum base resistance at high currents (in Ohms). (Default = RB). |
| RE | emitter resistance (in Ohms). (Default = 0). |
| RC | collector resistance (in Ohms). (Default = 0). |
| CJE | B-E zero-bias depletion capacitance (in Farads). (Default = 0). |
| VJE | B-E built-in potential (in Volts). (Default = 0.75) |
| MJE | B-E junction exponential factor (Default = 0.33). |
| TF | ideal forward transit time (in seconds). (Default = 0). |
| XTF | coefficient for bias dependence of TF (Default = 0). |
| VTF | voltage describing VBC dependence of TF (in Volts). (Default = infinite). |
| ITF | high-current parameter for effect on TF (in Amps). (Default = 0). |
| PTF | excess phase at freq=1.0/(TF*2PI) Hz (in Degrees). (Default = 0). |
| CJC | B-C zero-bias depletion capacitance (in Farads). (Default = 0). |
| VJC | B-C built-in potential (in Volts). (Default = 0.75). |
| MJC | B-C junction exponential factor (Default = 0.33). |
| XCJC | fraction of B-C depletion capacitance connected to internal base node (Default = 1). |
| TR | ideal reverse transit time (in seconds). (Default = 0). |
| CJS | zero-bias collector-substrate capacitance (in Farads). (Default = 0). |
| VJS | substrate junction built-in potential (in Volts). (Default = 0.75). |
| MJS | substrate junction exponential factor (Default = 0). |
| XTB | forward and reverse beta temperature exponent (Default = 0). |
| EG | energy gap for temperature effect on IS (in eV). (Default = 1.11). |
| XTI | temperature exponent for effect on IS (Default = 3). |
| KF | flicker noise coefficient (Default = 0). |
| AF | flicker noise exponent (Default = 1). |
| FC | coefficient for forward-bias depletion capacitance formula (Default = 0.5). |
| TNOM | parameter measurement temperature (in °C) - If no value is specified, the default value assigned to TNOM on the SPICE Options page of the Analyses Setup dialog will be used (Default = 27). |
Notes
- The model for the BJT is an adaptation of the integral charge control model of Gummel and Poon. This enhanced version of the original Gummel-Poon model includes several effects at high bias levels. When certain parameters are not specified, the model automatically defaults to that of the simpler Ebers-Moll model.
- Ground is used as the substrate node.
- The values for Initial B-E Voltage and Initial C-E Voltage only apply if the Use Initial Conditions option is enabled on the Transient/Fourier Analysis Setup page of the Analyses Setup dialog.
- The Area Factor affects the following model parameters:
- transport saturation current (
IS) - corner for forward beta high current roll-off (
IKF) - B-E leakage saturation current (
ISE) - corner for reverse beta high current roll-off (
IKR) - B-C leakage saturation current (
ISC) - zero bias base resistance (
RB) - current where base resistance falls halfway to its minimum value (
IRB) - minimum base resistance at high currents (
RBM) - emitter resistance (
RE) - collector resistance (
RC) - B-E zero-bias depletion capacitance (
CJE) - high-current parameter for effect on TF (
ITF) - B-C zero-bias depletion capacitance (
CJC) - zero-bias collector-substrate capacitance (
CJS)
If the Area Factor is omitted, a value of 1.0 is assumed.
- The link to the required model file (*.mdl) is specified on the Model Kind tab of the Sim Model dialog. The Model Name is used in the netlist to reference this file.
- Where a parameter has an indicated default (as part of the SPICE model definition), that default will be used if no value is specifically entered. The default should be applicable to most simulations. Generally you do not need to change this value.
Examples
Consider the BJT in the above image, with the following characteristics:
- Pin1 (collector) is connected to net
C - Pin2 (base) is connected to net
GND - Pin3 (emitter) is connected to net
E - Designator is
Q1 - The linked simulation model file is
2N3904.mdl.
If no values are entered for the parameters in the Sim Model dialog, the entries in the SPICE netlist would be:
*Schematic Netlist:
Q1 C 0 E 2N3904
.
.
*Models and Subcircuit:
.MODEL 2N3904 NPN(IS=1.4E-14 BF=300 VAF=100 IKF=0.025 ISE=3E-13 BR=7.5 RC=2.4
+ CJE=4.5E-12 TF=4E-10 CJC=3.5E-12 TR=2.1E-8 XTB=1.5 KF=9E-16 )
and the SPICE engine would use the indicated parameter information defined in the model file, along with default parameter values inherent to the model for those parameters not specified in the file.
If the following parameter values were specified on the Parameters tab of the Sim Model dialog:
- Area Factor =
3 - Starting Condition =
OFF - Temperature =
24
then the entries in the SPICE netlist would be:
*Schematic Netlist:
Q1 C 0 E 2N3904 3 OFF TEMP=24
.
.
*Models and Subcircuit:
.MODEL 2N3904 NPN(IS=1.4E-14 BF=300 VAF=100 IKF=0.025 ISE=3E-13 BR=7.5 RC=2.4
+ CJE=4.5E-12 TF=4E-10 CJC=3.5E-12 TR=2.1E-8 XTB=1.5 KF=9E-16 )
In this case, the SPICE engine would use this information, in conjunction with the indicated parameters defined in the model file (and any defaults for parameters not specified).
PSpice Support
Many of the parameters that can be included in a linked model file for this type of device are common to both Spice3f5 and PSpice. Those that are supported can be found in the previous section Parameters (definable within model file).
The following PSpice-based parameters are not supported for this device type:
| CN | quasi-saturation temperature coefficient for hole mobility |
| D | quasi-saturation temperature coefficient for scattering-limited hole carrier velocity |
| GAMMA | epitaxial region doping factor |
| ISS | substrate p-n saturation current |
| NK | high-current roll-off coefficient |
| NS | substrate p-n emission coefficient |
| QCO | epitaxial region charge factor |
| QUASIMOD | quasi-saturation model flag for temperature dependence |
| | epitaxial region resistance |
| | RB temperature coefficient (linear) |
| | RB temperature coefficient (quadratic) |
| | RC temperature coefficient (linear) |
| | RC temperature coefficient (quadratic) |
| | RE temperature coefficient (linear) |
| | RE temperature coefficient (quadratic) |
| TRM1 | RBM temperature coefficient (linear) |
| TRM2 | RBM temperature coefficient (quadratic) |
| VG | quasi-saturation extrapolated bandgap voltage at 0° K |
| VO | carrier mobility knee voltage |
| XCJC2 | fraction of CJC connected internally to Rb |
| XCJS | fraction of CJS connected internally to Rc |