Enhancement mode MOSFET is influenced by early effect that
arises in short channel devices. Since we are dealing with 180nm technology the
devices are prone to short channel effects. This channel length modulation
introduces an additional term in the MOSFET equation. It’s represented as ‘λ’
but is different from the device parameter used for expressing sizes of
transistor parts. It’s the inverse of early voltage. The implication can be
understood by observing the output characteristics. The curve influence by
channel length modulation will develop a slope corresponding to the early
voltage in the saturation region of the output characteristic of the NMOSFET. This
video gives a better explanation to the working of MOSFET and guides you
through the implementation of code and interpretation of graphs.
MATLAB CODE
%n-channel enhancement mode
MOSFET output characteristics
clear all;
%kn=un*cox = 100
microA/Volts
kn=1e-4;
%Let W/L= 2
W=360*(10^(-9));
L=180*(10^(-9));
beta=kn*W/L;
%Vth is the threshold
voltage
Vth=1;
%lambda is the inverse of
early voltage in voltage inverse
lambda=1/1000;
%Sweep drain to source
voltge from 0 to 10V
vds=0:0.5:10;
%Ask the user to enter gate
to source voltage
vgs=input('ENTER THE Vgs
in volts');
%Estimate length of the
array
m=length(vds);
for i=1:m
if vgs < Vth
current(1,i)=0;
current1(1,i)=0;
elseif vds(i) >=
(vgs - Vth)
current(1,i)=0.5* beta * ((vgs -
Vth)^2)*(1+lambda*vds(i));
current1(1,i)=0.5* beta * ((vgs -
Vth)^2);
elseif vds(i) <
(vgs - Vth)
current(1,i)=
beta*((vgs-Vth)*vds(i) - 0.5*(vds(i)^2))*(1+lambda*vds(i));
current1(1,i)=beta*((vgs-Vth)*vds(i)
- 0.5*(vds(i)^2));
end
end
plot(vds,current(1,:),'b',vds,current1(1,:),'r')
xlabel('Vds, V')
ylabel('Drain
Current,A')
title('I-V
Characteristics of a MOSFET')
OUTPUT CHARACTERISTICS
In this graph, the early voltage is 200V. So the effect is higher than the case following this. The output characteristics have been highly modified with the help og graph editor in MATLAB to help viewers explore them.
