Spice Syntax




Additional Information

More details can be found in the HyperSpice chapter in Extended Definitions for Advanced Users and Spice for Activate Users.


Q23 10 24 13 QMOD IC=0.6

Q50A 11 26 4 20 MOD1

The BJT device is a Bipolar Junction Transistor.

NC, NB, and NE are the collector, base, and emitter nodes, respectively.

NS is the (optional) substrate node. If unspecified, ground is used.

MNAME is the model name, AREA is the area factor, and OFF indicates an (optional) initial condition on the device for the dc analysis. If the area factor is omitted, a value of 1.0 is assumed.

The (optional) initial condition specification using IC=VBE, VCE is intended for use with the UIC option on the .TRAN control line, when a transient analysis is desired starting from other than the quiescent operating point. See the .IC control line description for a better way to set transient initial conditions.

The (optional) TEMP value is the temperature at which this device is to operate, and overrides the temperature specification on the .OPTION control line.


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.

Modified Gummel-Poon BJT Parameters:
name parameter units default example area
1 IS transport saturation current A 1.0e-16 1.0e-15 *
2 BF ideal maximum forward beta - 100 100
3 NF forward current emission coefficient - 1.0 1
4 VAF forward Early voltage V infinite 200
5 IKF corner for forward beta high current roll-off A infinite 0.01 *
6 ISE B-E leakage saturation current A 0 1.0e-13 *
7 NE B-E leakage emission coefficient - 1.5 2
8 BR ideal maximum reverse beta - 1 0.1
9 NR reverse current emission coefficient - 1 1
10 VAR reverse Early voltage V infinite 200
11 IKR corner for reverse beta high current roll-off A infinite 0.01 *
12 ISC leakage saturation current A 0 8
13 NC leakage emission coefficient - 2 1.5
14 RB zero bias base resistance Ω 0 100 *
15 IRB current where base resistance falls A infinite 0.1 *
halfway to its min value
16 RBM minimum base resistance at high currents Ω RB 10 *
17 RE emitter resistance Ω 0 1 *
18 RC collector resistance Ω 0 10 *
19 CJE B-E zero-bias depletion capacitance F 0 2pF *
20 VJE B-E built-in potential V 0.75 0.6
21 MJE B-E junction exponential factor - 0.33 0.33
22 TF ideal forward transit time sec 0 0.1ns
23 XTF coefficient for bias dependence of TF - 0
24 VTF voltage describing VBC V infinite
  dependence of TF
25 ITF high-current parameter A 0 *
  for effect on TF
26 PTF excess phase at freq=1.0/(TF*2PI) Hz deg 0
27 CJC B-C zero-bias depletion capacitance F 0 2pF *
28 VJC B-C built-in potential V 0.75 0.5
29 MJC B-C junction exponential factor - 0.33 0.5
30 XCJC fraction of B-C depletion capacitance - 1
  connected to internal base node
31 TR ideal reverse transit time sec 0 10ns
32 CJS zero-bias collector-substrate capacitance F 0 2pF *
33 VJS substrate junction built-in potential V 0.75
34 MJS substrate junction exponential factor - 0 0.5
35 XTB forward and reverse beta - 0
temperature exponent
36 EG energy gap for temperature eV 1.11
  effect on IS
37 XTI temperature exponent for effect on IS - 3
38 KF flicker-noise coefficient - 0
39 AF flicker-noise exponent - 1
40 FC coefficient for forward-bias - 0.5
  depletion capacitance formula
41 TNOM Parameter measurement temperature °C 27 50