According to one embodiment, a magnetic disk drive includes a notch filter, a parameter storage unit and a computation unit, when the sampling period changes from a first sampling period to a second sampling period, the computation unit computes a damping ratio parameter related to the damping ratio in a second set of parameters at the second sampling period, based on a first absolute value at a first angular frequency of a first transfer function computed from a first set of parameters at the first sampling period and a second absolute value at the first angular frequency of a second transfer function computed from the first set of parameters at the second sampling period, and the notch filter is set with the second set of parameters at the second sampling period is computed.

Apparatus and method for disturbance rejection in a control system. In some embodiments, a controller is adapted to position a control object. A disturbance observer generates a disturbance compensation value which is applied to reduce position error resulting from application of mechanical disturbance to the control object. The disturbance observer includes an adaptive filter with at least one dead zone providing a pass-through response with a scalar gain of less than one.

An apparatus may include a preamplifier configured to be connected to a plurality of magnetic read/write heads, wherein each of the magnetic read/write heads includes a read sensor to read data from a disc and a write element to write data to the disc. The preamplifier may include a first set of registers configured to indicate a first head of the plurality of magnetic read/write heads that is selected for reading data, a second set of registers configured to indicate a second head of the plurality of magnetic read/write heads that is selected for reading data, an input line configured to receive a control signal to activate reading data from the first head substantially simultaneously with reading data from the second head, a first output to provide data from the first head, and a second output to provide data from the second head.

A magnetic disc device according to an embodiment has a head, a position detector, and a filter unit. The position detector detects position information of the head on the basis of servo information. The filter unit performs filtering of an estimated frequency estimated by a quadratic adaptive digital filter that performs self-adaptation for a transfer function on the basis of positional difference information between position information and target position information of the head and adjusts all filter coefficients included in the transfer function on the basis of the estimated frequency.

A magnetic disc device according to an embodiment has a head, a position detector, and a filter unit. The position detector detects position information of the head on the basis of servo information. The filter unit performs filtering of an estimated frequency estimated by a quadratic adaptive digital filter that performs self-adaptation for a transfer function on the basis of positional difference information between position information and target position information of the head and adjusts all filter coefficients included in the transfer function on the basis of the estimated frequency.

A system for compensating RI while reading servo data from a rotating storage medium is provided and includes an equalizer, a Viterbi detector, and a servo control module. The equalizer receives a digital signal including a bit sequence of the servo data read from the rotating storage medium and equalizes the digital signal via filters. Some of the filters are to phase rotate the digital signal to generate phase rotated signals. The Viterbi detector operates based on a Viterbi state machine, which includes main branches having sub-branches, where: each of the main branches is to receive the phase rotated signals respectively at corresponding ones of the sub-branches; and the Viterbi detector is to determine branch metrics for each of the sub-branches, determine a minimum branch metric for each of the main branches, and process the minimum branch metric using an add-compare-select process to determine a most likely received bit sequence.

According to one embodiment, a magnetic disk device includes a loop shaping filter by a digital filter, which is disposed in parallel to a controller, having a peak at certain frequency, and coefficients of which are determined by a sensitivity function and a controlled object, wherein the coefficients of the loop shaping filter of the digital filter based on a change in a sampling period of servo information.

Systems and methods for compensating for hysteresis in a disc drive are described. In one embodiment, a method may use an inverse hysteresis model to linearize effects of hysteresis of a microactuator in the disc drive. The hysteresis model may be a Coleman-Hodgdon hysteresis model. The hysteresis of the microactuator may be characterized, and the inverse hysteresis model may be based at least in part on the characterization. The inverse hysteresis model may be used to implement a digital filter. The digital filter may be employed in series with the microactuator to linearize the effects of hysteresis.

Systems and methods for compensating for hysteresis in a disc drive are described. In one embodiment, a method may use an inverse hysteresis model to linearize effects of hysteresis of a microactuator in the disc drive. The hysteresis model may be a Coleman-Hodgdon hysteresis model. The hysteresis of the microactuator may be characterized, and the inverse hysteresis model may be based at least in part on the characterization. The inverse hysteresis model may be used to implement a digital filter. The digital filter may be employed in series with the microactuator to linearize the effects of hysteresis.

An apparatus includes a frequency analyzer circuitry, filter circuitry, and voice coil motor (VCM) control circuitry. The frequency analyzer circuitry is configured to detect one or more dominant frequencies of a position error signal (PES). The filter circuitry is configured to identify one or more filters in response to detecting the one or more dominant frequencies, apply the one or more identified filters to at least one of a microactuator control signal and PES, and generate a VCM compensation signal in response to the filtered PES or the microactuator control signal. The VCM control circuitry is configured to generate a VCM control signal in response to the VCM compensation signal.