Architecture for dc bias canceling and gain recovery for hard disk drive fly height detection

Abstract

According to an embodiment, a system for processing signals from a resistive sensor that monitors spacing between a disk drive head and disk surface includes a bias-canceling digital-to-analog converter and a translinear cell. The bias-canceling digital-to-analog converter generates a cancelation current equal to a bias current across the resistive sensor. The translinear cell receives the cancelation current and a composite current comprising the bias current and a sensor signal current, where the sensor signal current corresponds to variations in thermal conductivity as the disk drive head approaches the disk surface. The translinear cell generates differential output currents proportional to a sensing voltage while eliminating dependence on resistance value of the resistive sensor. A front-end circuit combines these differential output currents with signals coupled directly from sensor nodes at frequencies above a bias loop bandwidth.