Noise impact on servo TMR

The servo system of a hard disk drive operates under a very hostile environment and it needs to be robust and fast enough to minimize the position error variance during track following. The design and evaluation of the servo system performance relies heavily on the position error signal (PES) that is produced from a demodulation circuit. The electronic/magnetic noise that contaminates the PES produces its own nonrepetitive runout (NRRO). Furthermore, this noise can deceive our assessment of NRRO. In this paper, we present a spectral analysis of noise and address the pertinent issues of concern.