Signal processing in recording channels utilizing unshielded magnetoresistive heads

Because unshielded magnetoresistive (UMR) heads offer excellent short-wavelength sensitivity, immunity from Barkhausen noise, a velocity-independent readback signal, and simple construction, they were chosen for use in a new high-performance, multichannel tape system that operates at 80 kbit/in with a 1.5-mil track width. UMR heads have two properties that present a challenge to system designers: (1) a tendency to saturate with large applied magnetic fields, and (2) a high sensitivity to long-wavelength signals and noise which corresponds to an isolated pulse that extends far beyond the system's minimum transition time. These problems were solved through a combination of write and read equalization. System performance, measured by amplitude and timing margins, is shown to be excellent. In selecting write equalization parameters for amplitude-qualified peak-detecting systems, both amplitude and timing margins are significant. Write-equalized pulses that superficially appear to be highly irregular can frequently be effectively read equalized. The only caution in using write equalization is that write current risetime must be short enough to fully record the added pulses. This should not be a problem in systems with separately optimized write and read heads.<
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