Characterization of Write-Signal Efficiency Utilizing Write-Current Dynamic Wave-Shaping

The continued increase in disk-storage areal density creates challenges for the write-head design and the write-current wave shape to control the magnetic fields that are written on the disk's recording media. The preamplifier's write driver has programmable write-current controls, such as overshoot level, overshoot duration, baseline level, and rise/fall speeds for both the write transition and the overshoot relaxation to the write-current baseline level. These programmable write-current controls are used to achieve the desired magnetic track-print on the disk's recording media. Typically, the programmable write-current controls are independently set before the first write-data sequence (or sector) and may be adjusted between sectors. Another consideration is adjusting the write-current level as a function of its frequency and/or pattern. The write-current baseline level affects the written magnetic-core track width (MCW) on the media. A higher baseline level typically translates to a wider MCW. The other dominant parameter is the write-current overshoot level. The overshoot level affects the cross-track interference (XTI) as well as the MCW on the media. A higher overshoot level typically translates to a higher likelihood of XTI and a wider MCW. By implementing dynamic wave-shaping (DWS) as a function of the write data pattern, the XTI and MCW can be managed. This paper reviews the programmable write-current controls, the new architecture designed to implement DWS, the impact of write-current baseline and overshoot levels on XTI and MCW, and last the experimental data using DWS.