Flying height modulation estimation from pseudorandom readback signal in disk drives

In drive testing, pseudorandom data is very often used to avoid biasing results to a particular pattern, e.g., constant frequency. Using the readback signal to measure flying height modulation (FHM) is the most convenient method, but available methods need a special data pattern. In this paper, we present a method that can be used to measure FHM from a pseudorandom readback signal. The method was applied to measure the FHM due to slider-lubricant impact during read. The obtained FHM is a half-sinusoidal-like pulse with about 40 nm amplitude and 4 μs width that is very similar to results measured on spin-stand tests by using a laser Doppler vibrometer (LDV).