A Median Peak Detecting Servo Analog Processor For Hard Disk Drives

The demodulation of embedded servo signals in hard disk drives is traditionally achieved either by peak detection [1,2] or by area integration [3]. Peak detection has the advantage of simplicity. However, simple peak detection lacks immunity against impairments in the signal. Area integration provides high immunity against wide-band additive noise in the signal but does not eliminate local media defects that occur due to clustering of particles [l]. Also, it is likely to be affected by errors in the demodulation itself (such as in pulse count). which in turn are caused by noise in the signal . To overcome these limitations, this paper describes an analog processor that selects the median of up to five successive peaks. The five-peak median reduces random noise power by a factor of 3. It also completely eliminates local defects with density of less than 3 out of 5 and is insensitive to errors in pulse count.