This paper gives a design method of servo systems input signal,which is based on exact requires of stepping servo systems and combining of traditional form of input signal.

Based on some analysis on degenerative feedback technology in AMR Circuit, this article further explores the input signal in degenerative feedback AMR circuit, the ways to judge types of degenerative feedback by testing the depth of feedback, the working conditions of the ideal degenerative feedback and so on.

Taking into consideration the effects of input signal and the interference of model errors in deformation analysis,a new method of semiparametric AR model which considering the impacts of input signal is introduced.