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Slider Disk Asperity Hit Detector

IP.com Disclosure Number: IPCOM000122537D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 96K

Publishing Venue

IBM

Related People

Eaton, RE: AUTHOR [+4]

Abstract

Disclosed here is an electronic circuit for detecting in situ in a disk drive, slider-disk impacts based on the readback signal modulation that these impacts cause. The extra circuitry needed in a file to implement this technique encompasses only two, low-cost, commercially available integrated circuits: a frequency synthesizer and a heterodyne receiver.

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This is the abbreviated version, containing approximately 52% of the total text.

Slider Disk Asperity Hit Detector

      Disclosed here is an electronic circuit for detecting in
situ in a disk drive, slider-disk impacts based on the readback
signal modulation that these impacts cause.  The extra circuitry
needed in a file to implement this technique encompasses only two,
low-cost, commercially available integrated circuits: a frequency
synthesizer and a heterodyne receiver.

      A schematic diagram of the proposed circuitry is shown in Fig.
1.

      Written is a signal which on readback produces a constant
frequency signal with a fundamental frequency f. This readback signal
can be expressed in the following mathematical form: a(t) cos (wt)
b(t) cos (3wt) + c(t) cos (5wt) + .... . The amplitude a(t) of the
first harmonic line in the readback signal provides all information
to measure the slider lift-off by an asperity.

      To measure this amplitude a(t), the modified heterodyne
receiver of Fig. 1 is used.  The frequency of the input signal is
converted down to a crystal-controlled intermediate frequency (IF) of
0.5 MHz. A bandpass filter with a center frequency of 0.5 MHz and a
bandwidth of 200 kHz passes only the first harmonic signal. The
subsequent full- wave rectifier demodulates the amplitude a(t).  The
following low-pass filter determines the average amplitude a0. The
logarithm of the ratio of a(t) and a0 provides the slider-disk impact
signal.  This signal is proportional to the slider-disk clearance
variations and, therefore, contains the slider lift-off information.

      To avoid the disk rotation speed flutter from moving the
fundamental frequency out of the frequency detection window (+/- 100
kHz around the frequency chosen with the frequency synthesizer), the
frequency of the reference oscillator of the frequency synthesizer is
forced to follow the frequency flutter by means of a phase-locked
loop such...