Customizable Coherent Servo Demodulation for Disk Drives

This paper describes a servo demodulator which provides dramatically improved performance over the currently used servo demodulation methods for disk drives. The demodulation algorithm proposed here makes better use of knowledge about the readback signal coming from the disk to provide better noise immunity and more immunity to other non-idealities in the magnetic head response. The net result is a demodulated Position Error Signal (PES) which has a much cleaner response. 1 Introduction This paper describes an algorithm for servo demodulation in a disk drive that can significantly lower the Position Sensing Noise (PSN) that gets into the servo channel of a disk drive. It does this by mixing the servo burst signal with an idealized version of the dibit response and integrating over a finite, integral number of periods of the waveform. This di#ers from demodulation schemes which use rectifiers (almost all disk drives). It is also di#erent from the amplitude modulated (AM) signal demodul..