Abstract: A glide height test signal processor and method using increased high frequency components is disclosed. The processor is more sensitive to smaller asperities, maintains the positive characteristics of being monotonic and can be easily calibrated. The system includes a circuit for converting asperity contact to an electrical signal, a first bandpass circuit coupled to the first circuit, the first bandpass circuit having a first amplifier for amplifying the electrical signal by a first gain to generate a first amplified signal and a first filter for filtering the first amplified signal at a high frequency to generate a first filtered signal, wherein the first gain is selected for detection of asperities having a diameter of less than or equal to five microns and a processing circuit, coupled to the first bandpass circuit, for processing the first filtered signal to generate an indication of contact with an asperity having a diameter of less than or equal to five microns.

Abstract: A non-invasive servo-write system for use in a data recording disk drive. The system measures actuator position and generates a reference clock using semiconductor lasers. Internal position references are provided by reflective diffraction gratings affixed to the actuator arm and the spindle hub. Wavefront reconstruction optics correct for aberrations in the gratings. Optical sensors detect differential changes in the diffraction patterns created by the gratings, eliminating sensitivity to frequency drift. Decode electronics convert optical sensor data into an actuator position measurement. Control electronics drive the voice coil motor within the disk drive, which positions the write transducer to record servo information provided in a servo pattern generator. Transparent windows in the head-disk-assembly cover allow the servo-writer to write drives which are completely assembled and sealed.