Consider the LTIC system $$\begin{align*} \dot{x}(t)&=Ax(t)+Bu(t)\\ y(t)&=Cx(t)+Du(t) \end{align*}$$Then the observer-based controller $$\begin{align*} u(t)&=F\hat{x}(t)\\ \dot{\hat{x}}(t)&=(A+LC+BF+LDF)\hat{x}(t)-Ly(t) \end{align*}$$is s.t. the closed-loop system exactly has its eigenvalues at the eigenvalues of $A+BF$ and $A+LC$.