| 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.
|
.MODEL <model name> NPN [model parameters] .MODEL <model name> PNP [model 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 |
.MODEL QDEFAULT NPN
.MODEL QMOD PNP ( BF=80 )