BJT
- Updated2026-03-24
- 7 minute(s) read
BJT device instance declaration syntax:
Qxxx nodeCollector nodeBase nodeEmmiter <nodeBody>Model<area> <OFF> <IC=VBE0, VCE0>
BJT instance declaration parameters:
| Parameter Name | Parameter Description |
|---|---|
| area | Area factor. |
| OFF | [FLAG] Device is initially off. |
| ICVBE | Initial base-emitter voltage. |
| ICVCE | Initial collector-emitter voltage. |
| IC | Initial voltages. This is a two element vector alternate way of specifying ICVBE, ICVCE. |
| SENS_AREA | [FLAG] Flag to request sensitivity with respect to area. |
| TEMP | Instance temperature. |
BJT device NPN model definition syntax:
.MODEL mymodelname NPN <LEVEL=level> (<Other_Model_Parameters…> )
BJT device PNP model definition syntax:
.MODEL mymodelname PNP <LEVEL=level> (<Other_Model_Parameters…> )
BJT device LPNP model definition syntax:
.MODEL mymodelname LPNP (<Other_Model_Parameters…> )
The LEVEL parameter is used to select the appropriate BJT simulation model. Multisim provides two different BJT models, which are described below:
| Level Value | Description |
|---|---|
| 1 or BJT | Gummel-Poon model (DEFAULT model). |
| 4 or VBIC | VBIC model without self heating (Version 1.2). |
Depending on the Level value, different parameters for both instance declarations and model definitions are available.
The Gummel-Poon BJT model parameters are:
| Parameter Name | Parameter Description | Units | Default |
|---|---|---|---|
| AF | Flicker noise exponent. | — | 1.0 |
| BF | Ideal maximum forward beta. | — | 100.0 |
| BR | Ideal maximum reverse beta. | — | 1.0 |
| CJC | Base-collector zero bias depletion capacitance. | F | 0.0 |
| CJE | Base-emitter zero bias depletion capacitance. | F | 0.0 |
| CJS or CCS | Collector-substrate zero bias depletion capacitance. | F | 0.0 |
| CN | Quasi-saturation temperature coefficient for hole mobility. | — |
2.42 NPN |
| D | Quasi-saturation temperature coefficient for scattering-limited hole carrier velocity. | — |
0.87 NPN |
| EG | Bandgap voltage. | eV | 1.11 |
| FC | Forward bias depletion capacitance coefficient. | — | 0.5 |
| GAMMA | Epitaxial region doping factor. | — | 1x10-11 |
| IKF or IK | Corner for forward beta high current roll-off. | A | infinite |
| IKR | Corner for reverse beta high current roll-off. | A | infinite |
| IRB | Current at which base resistance is (RB+RBM)/2. | A | infinite |
| IS | Transport saturation current. | A | 1x10-16 |
| ISC | Base-collector leakage saturation current. | A | 0.0 |
| ISE | Base-emitter leakage saturation current. | A | 0.0 |
| ISS | Substrate junction saturation current. | A | 0.0 |
| ITF | High current dependence of TF. | A | 0.0 |
| KF | Flicker noise coefficient. | — | 0.0 |
| MJC or MC | Base-collector junction grading coefficient. | — | 0.33 |
| MJE or ME | Base-emitter junction grading coefficient. | — | 0.33 |
| MJS or MS | Substrate junction grading coefficient. | — | 0.0 |
| NC | Base-collector leakage emission coefficient. | — | 2.0 |
| NE | Base-emitter leakage emission coefficient. | — | 1.5 |
| NF | Forward current emission coefficient. | — | 1.0 |
| NK | High-current roll-off coefficient. | — | 0.5 |
| NR | Reverse current emission coefficient. | — | 1.0 |
| NS | Substrate junction emission coefficient. | — | 1.0 |
| PTF | Excess phase at 1/(2πTF) Hz. | ° | 0.0 |
| QCO | Epitaxial region charge factor. | C | 0.0 |
| QUASIMOD | Quasi-saturation model flag for GAMMA, RCO, and VO temperature dependence: = 1 perform temperature adjustment = 0 don't perform temperature adjustment | — | 0 |
| RB | Zero bias base resistance. | Ω | 0.0 |
| RBM | Minimum base resistance. | Ω | RB |
| RC | Collector resistance. | Ω | 0.0 |
| RCO | Epitaxial region resistance. | Ω | 0.0 |
| RE | Emitter resistance. | Ω | 0.0 |
| TF | Ideal forward transient time. | s | 0.0 |
| TNOM | Temperature at which model parameters were measured. | °C | — |
| TR | Ideal reverse transit time. | s | 0.0 |
| TRB1 | RB linear temperature coefficient. | 1/°C | 0.0 |
| TRB2 | RB quadratic temperature coefficient. | 1/(°C)2 | 0.0 |
| TRC1 | RC linear temperature coefficient. | 1/°C | 0.0 |
| TRC2 | RC quadratic temperature coefficient. | 1/(°C)2 | 0.0 |
| TRE1 | RE linear temperature coefficient. | 1/°C | 0.0 |
| TRE2 | RE quadratic temperature coefficient. | 1/(°C)2 | 0.0 |
| TRM1 | RBM linear temperature coefficient. | 1/°C | 0.0 |
| TRM2 | RBM quadratic temperature coefficient. | 1/(°C)2 | 0.0 |
| T_ABS | Absolute temperature. | °C | — |
| T_MEASURED | Temperature at which model parameters were measured. | °C | — |
| T_REL_GLOBAL | Temperature delta relative to global temperature. | °C | — |
| T_REL_LOCAL | Temperature delta relative to AKO model temperature. | °C | — |
| VAF or VA | Forward Early voltage. | V | infinite |
| VAR or VB | Reverse Early voltage. | V | infinite |
| VG | Quasi-saturation extrapolated bandgap voltage at 0K. | V | 1.206 |
| VJC or PC | Base-collector built in potential. | V | 0.75 |
| VJE or PE | Base-emitter built in potential. | V | 0.75 |
| VJS or PS | Substrate junction built in potential. | V | 0.75 |
| VO | Carrier mobility knee voltage. | V | 10.0 |
| VTF | Voltage giving VBC dependence of TF. | V | infinite |
| XCJC | Fraction of base-collector capacitance connected to internal base. | — | 1.0 |
| XCJC2 | Fraction of base-collector capacitance connected to internal base. | — | 1.0 |
| XCJS | Fraction of substrate-collector capacitance connected to internal collector. | — | 1.0 |
| XTB | Forward and reverse beta temperature exponent. | — | 0.0 |
| XTF | Coefficient for bias dependence of TF. | — | 0.0 |
| XTI | IS temperature effect exponent. | — | 3.0 |
The VBIC BJT model parameters are:
| Parameter Name | Parameter Description | Units | Default |
|---|---|---|---|
| AFN | B-E Flicker Noise Exponent. | — | 1.0 |
| AJC | B-C capacitance smoothing factor. | — | -0.5 |
| AJE | B-E capacitance smoothing factor. | — | -0.5 |
| AJS | S-C capacitance smoothing factor. | — | -0.5 |
| ART | Smoothing parameter for reach-through. | — | 0.1 |
| AVC1 | B-C weak avalanche parameter 1. | 1/V | 0.0 |
| AVC2 | B-C weak avalanche parameter 2. | 1/V | 0.0 |
| BFN | B-E Flicker Noise 1/f dependence. | — | 1.0 |
| CBCO | Extrinsic B-C overlap capacitance. | F | 0.0 |
| CBEO | Extrinsic B-E overlap capacitance. | F | 0.0 |
| CCSO | Fixed C-S capacitance. | F | 0.0 |
| CJC | Zero bias B-C depletion capacitance. | F | 0.0 |
| CJCP | Zero bias S-C capacitance. | F | 0.0 |
| CJE | Zero bias B-E depletion capacitance. | F | 0.0 |
| CJEP | B-C extrinsic zero bias capacitance. | F | 0.0 |
| CTH | Thermal capacitance. | J/K | 0.0 |
| DEAR | Delta activation energy for ISRR. | — | 0.0 |
| DTEMP | Local Temperature difference. | °C | 0.0 |
| EA | Activation energy for IS. | eV | 1.12 |
| EAIC | Activation energy for IBCI/IBEIP. | eV | 1.12 |
| EAIE | Activation energy for IBEI. | eV | 1.12 |
| EAIS | Activation energy for IBCIP. | eV | 1.12 |
| EANC | Activation energy for IBCN/IBENP. | eV | 1.12 |
| EANE | Activation energy for IBEN. | eV | 1.12 |
| EANS | Activation energy for IBCNP. | ev | 1.12 |
| EAP | Exitivation energy for ISP. | eV | 1.12 |
| EBBE | exp(-VBBE/(NBBE*Vtv)). | eV | 0.0 |
| FC | Fwd bias depletion capacitance limit. | — | 0.9 |
| GAMM | Epi doping parameter. | — | 0.0 |
| HRCF | High current RC factor. | — | 1.0 |
| IBBE | B-E breakdown current. | A | 1x10-6 |
| IBCI | Ideal B-C saturation current. | A | 1x10-6 |
| IBCIP | Ideal parasitic B-C saturation current. | A | 0.0 |
| IBCN | Non-ideal B-C saturation current. | A | 0.0 |
| IBCNP | Nonideal parasitic B-C saturation current. | A | 0.0 |
| IBEI | Ideal B-E saturation current. | A | 1x10-18 |
| IBEIP | Ideal parasitic B-E saturation current. | A | 0.0 |
| IBEN | Non-ideal B-E saturation current. | A | 0.0 |
| IBENP | Non-ideal parasitic B-E saturation current. | A | 0.0 |
| IKF | Forward knee current. | A | 0.0 |
| IKP | Parasitic knee current. | A | 0.0 |
| IKR | Reverse knee current. | A | 0.0 |
| IS | Transport saturation current. | A | 1x10-16 |
| ISP | Parasitic transport saturation current. | A | 0.0 |
| ISRR | Separate IS for fwd and rev. | A | 1.0 |
| ITF | High current dependence of TF. | A | 0.0 |
| KFN | B-E Flicker Noise Coefficient. | — | 0.0 |
| MC | B-C junction grading coefficient. | — | 0.33 |
| ME | B-E junction grading coefficient. | — | 0.33 |
| MS | S-C junction grading coefficient. | — | 0.33 |
| NBBE | B-E breakdown emission coefficient. | — | 1.0 |
| NCI | Ideal B-C emission coefficient. | — | 1.0 |
| NCIP | Ideal parasitic B-C emission coefficient. | — | 1.0 |
| NCN | Non-ideal B-C emission coefficient. | — | 2.0 |
| NCNP | Nonideal parasitic B-C emission coefficient. | — | 2.0 |
| NIE | Ideal B-E emission coefficient. | — | 1.0 |
| NEN | Non-ideal B-E emission coefficient. | — | 2.0 |
| NF | Forward emission coefficient. | — | 1.0 |
| NFP | Parasitic fwd emission coefficient. | — | 1.0 |
| NKF | High current beta rolloff. | — | 0.5 |
| NR | Reverse emission coefficient. | — | 1.0 |
| PC | B-C built in potential. | V | 0.75 |
| PE | B-E built in potential. | V | 0.75 |
| PS | S-C junction built in potential. | V | 0.75 |
| QBM | Select SGP qb formulation. | — | 0.0 |
| QCO | Epi charge parameter. | C | 0.0 |
| QTF | Variation of TF with base-width modulation. | — | 0.0 |
| RBI | Intrinsic base resistance. | Ω | 0.1 |
| RBP | Parasitic base resistance. | Ω | 0.1 |
| RBX | Extrinsic base resistance. | Ω | 0.1 |
| RCI | Intrinsic collector resistance. | Ω | 0.1 |
| RCX | Extrinsic collector resistance. | Ω | 0.1 |
| RE | Intrinsic emitter resistance. | Ω | 0.1 |
| RS | Intrinsic substrate resistance. | Ω | 0.1 |
| RTH | Thermal resistance. | K/W | 0.0 |
| TAVC | Temperature exponent of AVC2. | 1/K | 0.0 |
| TD | Forward excess-phase delay time. | s | 0.0 |
| TF | Ideal forward transit time. | s | 0.0 |
| TNBBE | Temperature coefficient of NBBE. | — | 0.0 |
| TNF | Temperature exponent of NF. | 1/K | 0.0 |
| TNOM | Parameter measurement temperature. | °C | 27.0 |
| TR | Ideal reverse transit time. | s | 0.0 |
| TVBBE1 | Linear temperature coefficient of VBBE. | — | 0.0 |
| TVBBE2 | Quadratic temperature coefficient of VBBE. | — | 0.0 |
| VBBE | B-E breakdown voltage. | V | 0.0 |
| VEF | Forward Early voltage. | V | 0.0 |
| VER | Reverse Early voltage. | V | 0.0 |
| VERS | Revision Version. | — | 1.2 |
| VO | Epi drift saturation voltage. | V | 0.0 |
| VREF | Reference Version. | — | 0.0 |
| VRT | Punch-through voltage of internal B-C junction. | V | 0.0 |
| VTF | Voltage giving VBC dependence of TF. | V | 0.0 |
| WBE | Portion of IBEI from Vbei, 1-WBE from Vbex. | — | 1.0 |
| WSP | Portion of ICCP. | — | 1.0 |
| XII | Temperature exponent of IBEI, IBCI, IBEIP, IBCIP. | — | 3.0 |
| XIKF | Temperature exponent of IKF. | — | 0.0 |
| XIN | Temperature exponent of IBEN, IBCN, IBENP, IBCNP. | — | 3.0 |
| XIS | Temperature exponent of IS. | — | 3.0 |
| XISR | Temperature exponent of ISR. | — | 0.0 |
| XRB | Temperature exponent of RB. | — | 0.0 |
| XRBI | Temperature exponent of RBI. | — | 0.0 |
| XRBP | Temperature exponent of RBP. | — | 0.0 |
| XRBX | Temperature exponent of RBX. | — | 0.0 |
| XRC | Temperature exponent of RC. | — | 0.0 |
| XRCI | Temperature exponent of RCI. | — | 0.0 |
| XRCX | Temperature exponent of RCX. | — | 0.0. |
| XRE | Temperature exponent of RE. | — | 0.0 |
| XRS | Temperature exponent of RS. | — | 0.0 |
| XTF | Coefficient for bias dependence of TF. | — | 0.0 |
| XVO | Temperature exponent of VO. | — | 0.0 |
SPICE implementation of VBIC was developed by Dr. Dietmar Warning, with contributions from authors of the NGSPICE project.
Additional Notes
The level parameter (level) must be a numerical constant—it may not contain parameters or expressions.
Examples
Q1 e b c 0 myBJT
.model myBJT NPN(vto=1.3)
Q2 e b c 0 myBJT2
.model myBJT2 PNP(LEVEL=4)