How to get a graph for DG MOSFET (Ids vs Vds characteristics)????

if true
  W=324;
un=1;
Cox=3;
Leff=6;
ld=3;
Ec=1;
lambda=25*10^(-5);
Vgs=0.5;
vth=2.04;
DIBL=0.5;
Vth=vth-DIBL
Vds=0:0.1:7%Vds Voltage value in Volts
Id=(2*W*un*Cox/Leff-ld+(Vds/Ec)) +(lambda* 2*W*Cox/(Leff-ld)^2)*((Vgs-Vth)*Vds-0.5*Vds^2)
plot(Vds,Id)
end

Answer 1

[Walter Roberson]

Id=(2*W*un*Cox/Leff-ld+(Vds/Ec)) +(lambda* 2*W*Cox/(Leff-ld).^2)*((Vgs-Vth)*Vds-0.5*Vds.^2)

[Akash Verma]

why .?

[Walter Roberson]

Vds=0:0.1:7

That is a 1 x 71 vector

Vds^2

That is the matrix power operator, equivalent in this case to

Vds * Vds

where * is the algebraic matrix product operation, also known as "inner product". When you have A * B for two matrices, then size(A,2) must equal size(B,1) -- the number of columns of the first matrix must match the number of rows of the second matrix. However when you take a (1 x 71) * (1 x 71) then the number of columns in the first operand is 71, but the number of rows in the second operand is 1. Using * (matrix power) between a 1 x 71 and a 1 x 71 is not a valid calculation.

If you consider for a second you will see that for A^2 to be valid, A must be a square matrix (possibly a scalar)

If you want each element of Vds to be independently squared then you need the element-by-element power, which is the .^ operator.