A 30 MHz low-noise CMOS preamplifier for disk drive heads

Data stored as magnetic flux reversals on a hard disk are read by an inductive head in close proximity to the disk, across which voltage signals of 0.1-1 mV are induced by the flux. These analog signals must be amplified before they are converted to logic levels by a decision circuit. A read-head preamplifier specially designed to be driven by an inductive source is used for this purpose. In a modern disk-drive subsystem, this amplifier must be wideband (>30 MHz), have a voltage gain of at least 100, and have low input noise (<2 nV/√Hz). The authors report on the first such amplifier fabricated in a 3-μm CMOS process. Some of the unique advantages offered by a CMOS design are highlighted, and its performance in a disk subsystem is compared with that of the industry standard bipolar preamplifier