Control systems/Closed loop systems

Close loop control systems use the open loop systems (as forward path) and feedback from the output to decide the input level to the open loop system. And because the input is decided based on how much away the output is from the desired level, the non idealities in forward path do not degrade the system performance. The accuracy of the output thus depends on the feedback path, which in general can be made very accurate.

For the open loop transfer function of $$G(s)$$, the closed loop transfer function is given by $$G(s)/(1+G(s)H(s))$$, where H(s) is the transfer function from output to input (with the loop broken).