GaAsFET (SPICE model)#

The GaAsFET (SPICE model) block is a SPICE model of a gallium arsenide field-effect transistor that implements three model levels. The block implements the following equivalent circuit, shown in Fig. 1 :

Thermal stress is calculated using the formula (1):

(1)#\[VT=\frac{k \cdot T}{q}\]

where:

\(k\) – Boltzmann constant, \(k=1.38 \cdot 10^{-23}\) [J/K];

\(T\) – diode temperature, [K];

\(q\) is the elementary electric charge of an electron, \(q=1.602 \cdot 10^{-19}\) [C].

Current \(I_d\) is calculated using the formulas:

For the first level model (Level 1):

cutoff region (\(U_{gs}\) ≤ VTO) (2) :

(2)#\[I_d=0\]

linear region and saturation region (\(U_{gs}\) > VTO) (3) :

(3)#\[I_d=BETA \cdot (1+ LAMBDA \cdot U_{ds}) \cdot (U_{gs} - VTO)^2 \cdot tanh(ALPHA \cdot U_{ds})\]

For the second level model (Level 2):

cutoff region (\(U_{gs}\) ≤ VTO) (2);
linear region and saturation region (\(U_{gs}\) > VTO) (4) :

(4)#\[\begin{split} Kt =\begin{cases}1-(1-\frac{U_{ds}\cdot ALPHA}{3})^3 , & \ 0<U_{ds}<\frac{3}{ALPHA}\\1, & U_{ds}\geq \frac{3}{ALPHA} \end{cases} \\ I_d=BETA \cdot (1+LAMBDA \cdot U_{ds})\cdot (U_{gs}- VTO)^2 \cdot \frac{Kt}{(1+B \cdot (U_{gs}-VTO))} \end{split}\]

For the third level model (Level 3):

cutoff region (\(U_{gs}\) ≤ VTO) (2);
linear region and saturation region (\(U_{gs}\) > VTO) (5) :

(5)#\[\begin{split} Kt =\begin{cases}1-(1-\frac{U_{ds}\cdot ALPHA}{3})^3 , & \ 0<U_{ds}<\frac{3}{ALPHA}\\1, & U_{ds}\geq \frac{3}{ALPHA} \end{cases} \\ I_{dso}=BETA \cdot (U_{gs} - (VTO - GAMMA \cdot U_{ds}))^Q \cdot Kt \\ I_d=\frac{I_{dso}}{(1+DELTA \cdot U_{ds} \cdot I_{dso})} \end{split}\]

The equivalent circuit capacitances are calculated using the formulas:

For the first level model (Level 1) (6) :

(6)#\[\begin{split}C_{gs}=\begin{cases}\frac{CGS}{(1-\frac{U_{gs}}{VBI})^M} , & \ U_{gs}\leq FC \cdot VBI\\CGS \cdot (1-FC)^{-(1+M)}\cdot (1-FC \cdot (1+M)+M \cdot (\frac{U_{gs}}{VBI})), & U_{gs}> FC \cdot VBI \end{cases} \\C_{gd}=\begin{cases}\frac{CGD}{(1-\frac{U_{gd}}{VBI})^M} , & \ U_{ds}\leq FC \cdot VBI\\CGD \cdot (1-FC)^{-(1+M)}\cdot (1-FC \cdot (1+M)+M \cdot (\frac{U_{gd}}{VBI})), & U_{ds}> FC \cdot VBI \end{cases}\end{split}\]

For Level 2 and Level 3 models (7) :

(7)#\[\begin{split}Ve=\frac{(U_{gs}+U_{gd}+\sqrt{(U_{gs}-U_{gd})^2+\frac{1}{ALPHA^2}})}{2}\\Vn.pre=\frac{(Ve + VTO + \sqrt{(Ve-VTO)^2+DELTA^2)}}{2}\\Vn=\begin{cases}\ Vn.pre , & \ Vn.pre<VMAX\\VMAX, & Vn.pre\geq VMAX \end{cases}\\K1=\frac{1+ \frac{Ve-VTO}{\sqrt{(Ve-VTO)^2+VDELTA^2}}}{2}\\K2=\frac{1+ \frac{U_{gs}-U_{gd}}{\sqrt{(U_{gs}-U_{gd})^2+\frac{1}{ALPHA^2}}}}{2}\\K3=\frac{1-\frac{U_{gs}-U_{gd}}{\sqrt{(U_{gs}-U_{gd})^2+\frac{1}{ALPHA^2}}}}{2}\\Cgs=\frac{CGS \cdot K1 \cdot K2}{\sqrt{1-\frac{Vn}{VBI}}}+CGD \cdot K3\\Cgd=\frac{CGS \cdot K1 \cdot K3}{\sqrt{1-\frac{Vn}{VBI}}}+CGD \cdot K2\end{split}\]

1. Properties#

Property	Default Value	Description	Units of measurement
Level of model: Level 1; Level 2; Level 3	Level 1	–	–
AREA - device area	1.0	–	–
VTO - pinch-off voltage	-2.5	–	V
ALPHA - saturation voltage parameter	2.0	–	V\(^{-1}\)
BETA - transconductance coefficient	0.1	–	А/V\(^2\)
B - doping tail extender	0.3	–	V\(^{-1}\)
LAMBDA - channel-length modulation	0.0	–	V\(^{-1}\)
GAMMA - static feedback parameter	0.0	–	–
DELTA - output feedback parameter	0.0	–	V\(^{-1}\)
Q - power law parameter	2.0	–	–
RG - gate ohmic resistance	0.0	–	Ohm
RD - drain ohmic resistance	0.0	–	Ohm
RS - source ohmic resistance	0.0	–	Ohm
IS - gate pn saturation current	1.0E-14	–	А
N - gate pn emission coefficient	1.0	–	–
M - gate pn grading coefficient	0.5	–	–
VBI - gate pn potential	1.0	–	V
CGD - zero-bias gate-drain pn cap.	1.0E-9	–	F
CGS - zero-bias gate-source pn cap.	1.0E-9	–	F
CDS - fixed drain-source cap.	1.0E-9	–	F
FC - forward-bias depletion coeff.	0.5	–	–
VDELTA - capacitance transition volt.	0.2	–	V
VMAX - capacitance limiting voltage	0.5	–	V
EG - bandgap voltage	1.12	–	eV
XTI - temperature coefficient of IS	0.0	–	–
VTOTC - temperature coefficient of VTO	0.0	–	V/°C
BETATCE - exp. temperature coeff. of BETA	0.0	–	%/°C
TRG1 - temperature coefficient of RG	0.0	–	°C⁻¹
TRD1 - temperature coefficient of RD	0.0	–	°C⁻¹
TRS1 - temperature coefficient of RS	0.0	–	°C⁻¹
T - device operating temperature	27.0	–	°C
Tnom - temperature at which the model parameters are measured	27.0	–	°C

2. Inputs and outputs#

Parameters	Input/Output	Description	Units of measurement	Port type
Drain	Input	-	-	Electronics
Gate	Input	-	-	Electronics
Source	Output	-	-	Electronics

In order to see the connection capabilities of the block, you need to go to page Description of block ports