The following table contains the model parameters for the JFET model.
Name  Symbol  Description  Unit  Default 
Vt0  zero bias threshold voltage  
Beta  transconductance parameter  
Lambda  channellength modulation parameter  
Rd  drain ohmic resistance  
Rs  source ohmic resistance  
Is  gatejunction saturation current  
N  gate PN emission coefficient  
Isr  gatejunction recombination current parameter  
Nr  Isr emission coefficient  
Cgs  zerobias gatesource junction capacitance  
Cgd  zerobias gatedrain junction capacitance  
Pb  gatejunction potential  
Fc  forwardbias junction capacitance coefficient  
M  gate PN grading coefficient  
Kf  flicker noise coefficient  
Af  flicker noise exponent  
Ffe  flicker noise frequency exponent  
Temp  device temperature  
Xti  saturation current exponent  
Vt0tc  Vt0 temperature coefficient  
Betatce  Beta exponential temperature coefficient  
Tnom  temperature at which parameters were extracted  
Area  default area for JFET 
The current equation of the gate source diode and its derivative writes as follows:
(10.37)  
(10.38) 
The current equation of the gate drain diode and its derivative writes as follows:
(10.39)  
(10.40) 
Both equations contain the gatejunction saturation current , the gate PN emission coefficient and the temperature voltage with the Boltzmann's constant and the electron charge . The operating temperature must be specified in Kelvin.
(10.41) 
The controlled drain currents have been defined by Shichman and Hodges [13] for different modes of operations.
and with  (10.42) 
(10.43)  
(10.44)  
(10.45)  
normal mode, saturation region:
 
(10.46)  
(10.47)  
(10.48)  
normal mode, linear region:
 
(10.49)  
(10.50)  
(10.51) 
(10.52)  
(10.53)  
(10.54)  
inverse mode, saturation region:
 
(10.55)  
(10.56)  
(10.57)  
inverse mode, linear region:
 
(10.58)  
(10.59)  
(10.60) 
The MNA matrix entries for the voltage controlled drain current source can be written as:


controlling nodes  
D 

S 

controlled nodes 
With the accompanied DC model shown in fig. 10.7 using the same principles as explained in section 3.3.1 on page it is possible to build the complete MNA matrix of the intrinsic JFET.
Applying the rules for creating the MNA matrix of an arbitrary network the complete MNA matrix entries (admittance matrix and current vector) for the intrinsic junction FET are:
(10.61) 
with
(10.62)  
(10.63)  
(10.64) 
The small signal Yparameter matrix of the intrinsic junction FET writes as follows. It can be converted to Sparameters.
(10.65) 
with
(10.66)  
(10.67)  
(10.68) 
The junction capacitances are modeled with the following equations.
(10.69)  
(10.70) 
Both the drain and source resistance and generate thermal noise characterized by the following spectral density.
(10.71) 
Channel noise and flicker noise generated by the DC transconductance and current flow from drain to source is characterized by the following spectral density.
(10.72) 
The noise current correlation matrix (admittance representation) of the intrinsic junction FET can be expressed by
(10.73) 
This matrix representation can be easily converted to the noisewave representation if the small signal Sparameter matrix is known.
Temperature appears explicitly in the exponential terms of the JFET model equations. In addition, saturation current, gatejunction potential and zerobias junction capacitances have builtin temperature dependence.
(10.74)  
(10.75)  
(10.76)  
(10.77)  
(10.78) 
where the dependency has already been described in section 10.2.4 on page . Also the threshold voltage as well as the transconductance parameter have a temperature dependence determined by
(10.79)  
(10.80) 
The area factor used for the JFET model determines the number of equivalent parallel devices of a specified model. The following parameters are affected by the area factor.
(10.81)  
(10.82)  
(10.83) 