Create a vector out of the ‘vgs’ quantities you want to plot:
vgs=[0.7 1 1.5 2];
then use a second loop to index them:
W=40;
Vth=0.45;
Leff=0.15;
k=4.255*(10^-4)*(W/Leff);
lambda=25*10^-5;
Vds=linspace(0,2.5);
vgs=[0.7 1 1.5 2];
m=length(Vds);
for k1 = 1:numel(vgs)
for i=1:m
if vgs(k1) < Vth
current(k1,i)=0;
elseif Vds(i) >= (vgs(k1) - Vth)
current(k1,i)=0.5* k * ((vgs(k1) - Vth).^2);
elseif Vds(i) < (vgs(k1) - Vth)
current(k1,i)= k*((vgs(k1)-Vth)*Vds(i) - 0.5*(Vds(i).^2));
end
end
end
figure
plot(Vds,current, 'LineWidth',1.5)
grid
legend(compose('V_{GS} = %0.1f V', vgs), 'Location','NW')
