Junction Field-Effect Transistor (JFET) Model
Model Kind
Transistor
Model Sub-Kind
JFET
SPICE Prefix
J
SPICE Netlist Template Format
@DESIGNATOR %1 %2 %3 @MODEL &"AREA FACTOR" &"STARTING CONDITION" ?"INITIAL D-S VOLTAGE"|IC=@"INITIAL D-S VOLTAGE", @"INITIAL G-S 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 D-S Voltage | time-zero voltage across Drain-Source terminals (in Volts). |
| Initial G-S Voltage | time-zero voltage across Gate-Source terminals (in Volts). |
| Temperature | temperature at which the device is to operate (in Deg. C). 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:
| VTO | threshold voltage VTO (in Volts). (Default = -2.0). |
| BETA | transconductance parameter β (in A/V 2 ). (Default = 1.0e-4) |
| LAMBDA | channel-length modulation parameter λ (in 1/V). (Default = 0). |
| RD | drain ohmic resistance (in Ohms). (Default = 0). |
| RS | source ohmic resistance (in Ohms). (Default = 0). |
| CGS | zero-bias G-S junction capacitance C GS (in Farads). (Default = 0). |
| CGD | zero-bias G-D junction capacitance C GD (in Farads). (Default = 0). |
| PB | gate junction potential (in Volts). (Default = 1). |
| IS | gate junction saturation current I S (in Amps). (Default = 1.0e-14). |
| B | doping tail parameter (Default = 1). |
| 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) |
Notes
- The model for the JFET is based on the FET model of Shichman and Hodges.
- The values for the Initial D-S Voltage and Initial G-S 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:
- transconductance parameter (
BETA) - drain ohmic resistance (
RD) - source ohmic resistance (
RS) - zero-bias G-S junction capacitance (
CGS) - zero-bias G-D junction capacitance (
CGD) - gate junction saturation current (
IS)
- If the Area Factor is omitted, a value of
1.0is 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 JFET in the above image, with the following characteristics:
- Pin1 (Drain) is connected to net D
- Pin2 (Gate) is connected to net
G - Pin3 (Source) is connected to net
S - Designator is
J1 - The linked simulation model file is
2N4393.mdl.
If no values are entered for the parameters in the Sim Model dialog, the entries in the SPICE netlist would be:
*Schematic Netlist:
J1 D G S 2N4393
.
.
*Models and Subcircuit:
.MODEL 2N4393 NJF(VTO=-1.422 BETA=0.009109 LAMBDA=0.006 RD=1 RS=1 CGS=4.06E-12
+ CGD=4.57E-12 IS=2.052E-13 KF=1.23E-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 = 4
- Temperature = 29
then the entries in the SPICE netlist would be:
*Schematic Netlist:
J1 D G S 2N4393 4 TEMP=29
.
.
*Models and Subcircuit:
.MODEL 2N4393 NJF(VTO=-1.422 BETA=0.009109 LAMBDA=0.006 RD=1 RS=1 CGS=4.06E-12
+ CGD=4.57E-12 IS=2.052E-13 KF=1.23E-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
To make this device model compatible with PSpice, the following additional model parameters are supported and can be entered into a linked model file (*.mdl) for the device:
| ALPHA | ionization coefficient (in Volt-1). (Default = 0). |
| BETATCE | BETA exponential temperature coefficient (in Amp/Volt2). (Default = 1E-4). |
| ISR | gate p-n recombination current parameter (in Amps). (Default = 0). |
| M | gate p-n grading coefficient. (Default = 0.5). |
| N | gate p-n emission coefficient. (Default = 1). |
| NR | emission coefficient for isr. (Default = 2). |
| VK | ionization knee voltage (in Volts). (Default = 0). |
| VTOTC | VTO temperature coefficient (in Volt/˚C). (Default = 0). |
| XTI | IS temperature coefficient. (Default = 3). |
Where a parameter has an indicated default, that default will be used if no value is specifically entered.
The format for the PSpice model file is:
.MODEL ModelName NJF(Model Parameters) - N-channel JFET.MODEL ModelName PJF(Model Parameters) - P-channel JFET
where
ModelNameis the name of the model, the link to which is specified on the Model Kind tab of the Sim Model dialog. This name is used in the netlist (@MODEL) to reference the required model in the linked model file.Model Parametersare a list of supported parameters for the model, entered with values as required.
For an example of using a PSpice-compatible diode model in a simulation, refer to the example project JFET.PrjPCB.