Skew-Dependent Performance Evaluation of Array-Reader-Based Magnetic Recording With Dual-Reader

Abstract

Array-reader-based magnetic recording (ARMR) shows potential to achieve areal density capability (ADC) beyond 1 Tb/in 2 by jointly processing multiple readback streams. Dual-reader ARMR with two read sensors and associated read channel signal processing algorithms are currently being actively investigated. In this paper, dual-reader ARMR performance is evaluated focusing on skewinduced variation in cross-track separation (CTS) between the two read sensors. Spin-stand captured waveforms based evaluation is presented for the cases where a dual-reader with certain CTS and skew is emulated using captures from a single-reader at different cross-track locations as well as for the case of actual dual-reader-based captures, where the latter also accounts for head rotation. Based on bit error rate scan along cross-track under various squeezed recording and skew conditions, squeeze-to-death margin-based ADC gain of ARMR is predicted. Dual-reader ARMR shows 5%-10% ADC gain over single-reader for CTS less than 0.6 track pitch, while showing limited gains for larger CTS. Also presented is the performance evaluation of dual-reader ARMR on spin-stand using a hardware accelerated ARMR performance evaluation platform, called Stingray, which uses four Avago read channel silicon chips and a customized field programmable gate array to enable high-speed joint equalization and detection using dual-reader readback streams.Index Terms-2-D equalizer, array-reader, array-reader-based magnetic recording (ARMR), hard disk drives (HDDs), two-dimensional magnetic recording (TDMR).

Advanced channel signal processing for multi-track or multi-wordline data storage systems

“…For array readers, the skew not only deviates the reader from the tangential of moving direction but also variates the CTS between readers since the reader assembly rotates together. The CTS with the skew angle θ for dual reader is investigated in [17], which can be extended for three readers as below,…”

“…Additional readers may improve the servo performance by taking advantage the new information [8], and yields faster random access and favorable gains with other performance measures. On the other hand, skew may degrade the performance gain of ARMR by changing the cross-track separation (CTS) between readers broadly and may result in unfavorable CTS for particular skew angles [17]. Especially for the multi-track system, the skew effect is worse since the CTS variation becomes larger when simultaneously reading multiple tracks and the information for the jointly processing tracks is not necessarily clear and balanced.…”

Effect of Reader Sensitivity Rotation in TDMR With Head Skew

“…Therefore it is possible that the bit error rate (BER) performance is improved by fitting reader sensitivity to the bit shape. In this paper, we evaluate the effect of reader sensitivity rotation in the TDMR R/W channel with head skew [7] under a specification of 4 Tbit/inch 2 by computer simulation applying the low-density parity-check (LDPC) coding and iterative decoding system with the two-dimensional finite impulse response (TD-FIR) filter.…”