On a method for characterizing read sensor nonlinearity using read-back signals

The magnetic transducer that forms the active element of the read head is intrinsically nonlinear. Through careful design and manufacturing sensor nonlinearity can be controlled however it is always present to some degree. The sensor transfer function can be measured by applying a known external field to the head in a quasi-static tester. It is sometimes helpful to be able to estimate the head transfer function, in-situ on a spin-stand or in a drive by analyzing read-back signals. Sensor nonlinearity produces characteristic echoes when dibit extraction is performed. These echoes give an indication of the presence of distortion but are difficult to interpret precisely. In this paper a method is presented for using PRBS patterns to estimate the shape of the head transfer function.