Design considerations for high data-rate pre-amplifiers for use in a disk-drive

In an effort to achieve higher data-rates in disk-drives, it has been proposed that moving the preamp closer to the head will improve writer performance. This paper shows that the opposite is true: moving the writer closer to the head degrades write current rise-time and overshoot. Although settling time is improved by moving the preamp closer to the head, impedance-matching techniques are sufficient to address this. Ironically, reader considerations may motivate Chip-On-Suspension (COS), but only for MR sensors that are either very high or very low impedance. This paper will detail the noise peaking that results from an impedance-mismatched reader input network. Both reader and writer performances can be improved by using novel architectures and by optimizing their respective interconnects.