United States Patent  [u] Patent Number: 5,068,754
Garde  Date of Patent: Nov. 26, 1991
 METHOD AND APPARATUS FOR MEASURING BIT SHIFT
 Inventor: Lawrence Garde, Bloomington, Minn.
 Assignee: Seagate Technology, Inc., Scotts Valley, Calif.
 Appl. No.: 440,662
 Filed: Not. 22,1989
 Int. CI.' G11B 5/09
 U.S. Q 360/45; 360/31
 Field of Search 360/45, 31; 324/212
 References Cited
U.S. PATENT DOCUMENTS
3,686,682 8/1972 Behr et al. .
4,612,586 9/1986 Sordello et al. .
4,799,112 1/1989 Bremmer et al 360/31
"Phase Margin Analysis is Critical to Disk-Drive Test", Oct. 1989; Electronic Test Magazine, pp. 30-32, 38.
Primary Examiner—Vincent P. Canney
Attorney, Agent, or Firm—Kinney & Lange
A method and apparatus for measuring aggregate bit shift (peak shift) timing error in the readback signal of a magnetic storage system. The method provides an effective measure of the relative goodness of one magnetic head with respect to another magnetic head. A repetitive data pattern is written onto a magnetic disk. The magnetic head under test reads back the magnetic transitions from the disk. The signals are amplified, detected and digitized. A low cost gating system synchronizes to the recorded data pattern and outputs a pulse at the beginning and end of a selected period corresponding to two transitions in the data pattern. A time interval measuring device connected at the output of the gating system determines the average time or time variance between the beginning and end data pulses. The average time value correlates to the aggregate bit shift inherent in the magnetic read head being measured. This relatively simple system provides fast, low cost, accurate bit shift measurement.
22 Claims, 6 Drawing Sheets