How to write this constraint in CVX

Actually, b, B, A are vectors of dimension M.

I try to write like this:

for i = 1:M

% b(i,1) >= (2^B(i)-1)^2/Alength(i)^2;

[1, t(i); t(i), b(i,1)*Alength(i,1)^2] >= 0

t(i) >= 2^B(i,1)-1

end

But CVX gives me the error message as

Who can tell me why? Thanks in advance.