The JFET (Junction Field-Effect Transistor) is a three-terminal semiconductor device controlled by a voltage applied to the gate-source junction.
J<name> <drain> <gate> <source> <model_name> [<area>] [OFF] [IC=<vds>[,<vgs>]]
| Parameter | Description |
|---|---|
drain |
Drain node |
gate |
Gate node |
source |
Source node |
model_name |
Name of a .MODEL NJF(...) or .MODEL PJF(...) definition |
area |
Area factor |
OFF |
Initial guess: device is off |
IC=vds[,vgs] |
Initial junction voltages for UIC |
J1 DRAIN GATE SOURCE J2N3819
J2 D G S my_njfet 2.0
A JFET is nonlinear. Its drain current depends on gate-source and drain-source voltage, and its gate junction behaves diode-like. During Newton iteration, SpiceSharp linearizes those equations around the current voltage guess.
Conceptually, the JFET contributes:
| Term | MNA role |
|---|---|
| Channel conductance | Matrix slope between drain and source. |
| Transconductance | Controlled-source Jacobian term from gate voltage. |
| Gate junction conductance | Diode-like matrix and RHS terms. |
| Gate capacitances | AC admittance terms or transient companion terms. |
The stamp therefore changes as the operating point moves. .AC uses the
small-signal derivatives from the solved operating point, while .TRAN also
integrates any capacitance terms.
For the deeper solver picture, see How SpiceSharp Solves Circuits.
.MODEL J2N3819 NJF(VTO=-3 BETA=1.304m LAMBDA=2.25m IS=33.57f CGS=2.414p CGD=0.3p)
| Parameter | Description |
|---|---|
VTO |
Pinch-off voltage |
BETA |
Transconductance coefficient |
LAMBDA |
Channel-length modulation |
IS |
Gate junction saturation current |
CGS |
Gate-source capacitance |
CGD |
Gate-drain capacitance |
RD |
Drain resistance |
RS |
Source resistance |