Analog Frontend for Tribo-Current-Based Fly-Height Sensor for Magnetic Hard Disk Drive

This paper presents an analog front end for measuring the triboelectric current flow between the triboelectric current sensor attached to the magnetic recording head and the media in a hard-disk-drive (HDD) system. The magnitude of the triboelectric current serves as a measure of the proximity between the head and the media and can be optimized for better performance in the next generation HDDs. The analog front end employs a novel current-divert circuit to create two separate signal paths with high and low gain that together provide a linear measure of the triboelectric current over a large dynamic range. A 42.6-M Omega dc-coupled, low leakage transimpedance amplifier is designed for the high gain path. It employs an area-efficient, floating, gate-voltage controlled MOS resistor with a novel open-loop temperature compensation scheme. A gain variation of < 10% and an input current offset drift of < +/- 35 pA are measured over a temperature range of -40 degrees C to 120 degrees C. With the help of the low gain path, an overall input dynamic range of tens of picoamps to 50 nA is achieved. The high accuracy and large dynamic range measurement of tribocurrent serves the dual purpose of accurate fly-height estimation and tracking of the topography of the hard-disk media.