System and method for measuring readback signal amplitude asymmetry in a perpendicular magnetic recording disk drive

A method of operating a head-disk tester having a spectrum analyzer, a processor, and memory accessible by the processor, the tester being capable of supporting a rotatable perpendicular magnetic recording disk and a read/write head for writing magnetizations generally perpendicularly on the disk and reading written magnetizations from the disk, the processor-implemented method comprising:

• generating a signal to the head to cause the head to write a first pattern on the disk, said first pattern comprising a series of isolated regions magnetized in a first direction and separated by baseline regions of alternating first-direction and second-direction magnetizations, said second direction being generally opposite to said first direction;
• generating a signal to the head to cause the head to write a second pattern on the disk, said second pattern comprising a series of isolated regions magnetized in said second direction and separated by baseline regions of alternating first-direction and second-direction magnetizations;
• directing the head to read said first pattern to generate a first readback signal;
• directing the head to read said second pattern to generate a second readback signal;
• measuring with the spectrum analyzer the amplitude of the pulses in said first readback signal;
• measuring with the spectrum analyzer the amplitude of the pulses in said second readback signal;
• and
• calculating from said measured amplitudes the asymmetry between the first readback signal amplitude and the second readback signal amplitude.

A computer program product for operating a head-disk tester capable of supporting a magnetic recording disk and adapted for connection to a write head for writing magnetizations on the disk and to a read head for detecting magnetizations from the disk, the computer program product comprising:

• a computer-readable medium;
• and
• computer-executable program code embodied in the computer-readable medium for
• signaling the write head to write a series of isolated regions magnetized in a first direction;
• signaling the write head to write a series of isolated regions magnetized in a second direction generally opposite said first direction;
• detecting a first readback signal from the read head representing the regions magnetized in said first direction;
• detecting a second readback signal from the read head representing the regions magnetized in said second direction;
• measuring in the frequency domain the amplitude of the first readback signal;
• measuring in the frequency domain the amplitude of the second readback signal;
• and
• calculating from said measured amplitudes the asymmetry between the first readback signal amplitude and the second readback signal amplitude.