Designing disk drive interconnects to obtain a desired transmitted write current waveform

This paper describes the application of nonuniform transmission lines as interconnects for disk drive applications. The design method that we use is a direct optimization, approximating the interconnect as a cascade of piecewise uniform transmission line segments. Models for the write head, interconnect, and write driver are provided. We find nonuniform interconnects are most effective for low-turn heads (<5 turns). We explore nonuniform interconnects as a way of inducing write current overshoot with short settling times (i.e., minimal ringing). For interconnects with total (one-way) propagation delay t_d, the effective overshoot duration ranges from 2t_d to 100 ps. The effective overshoot amplitude is <50%. The waveforms generated by nonuniform interconnects are limited primarily by the constraint on the interconnect length. Any additional mechanical constraints on specific regions of the interconnect may cause the design impedance profile to be compromised. If this is the case, multiple smaller constrained regions are preferred to a single large region.