Ideals whose associated graded rings are isomorphic to the base rings

Let $k$ be a field. We determine the ideals $I$ in a finitely generated graded $k$-algebra $A$, whose associated graded rings are isomorphic to $A$. Also we compute the graded local cohomologies of the Rees rings $A[It]$ and give the condition for $A[It]$ to be generalized Cohen-Macaulay.