Abstract: An apparatus including a photo detector circuit, a first circuit, a second circuit and a third circuit. The photo detector circuit may be configured to generate an RF signal in response to a laser spot on a surface of an optical disc. The first circuit may be configured to generate a first digital signal in response to an AC-coupled version of the RF signal. The second circuit may be configured to generate a second digital signal in response to a DC-coupled version of the RF signal. The third circuit may be configured to generate one or more detect signals in response to the first digital signal and the second digital signal. Each of the one or more detect signals may indicate a respective condition of the surface of the optical disc.

Abstract: An apparatus comprising an analog-to-digital converter, a compensation circuit, a partial response equalizer and a non-adaptive Viterbi decoder. The analog-to-digital converter may be configured to convert an input analog signal into a digital signal. The compensation circuit may be configured to generate an output signal by clipping the digital signal. The partial response equalizer circuit may be configured to shape the output signal into a pre-defined target with a delay operator. The decoder may be configured to calculate a minimum error between data in the output signal and other possible data sequences.

Abstract: A method and apparatus for servowriting using a unipolar write current is disclosed. A track for writing a servo pattern is determined and the servo pattern is written using a unipolar write current pulse. The writing of the servo pattern using the unipolar write current pulse creates a servo pattern having less of an erase band and wider track width than if the servo pattern was produced by a bipolar write current pulse. The unipolar write current pulse is applied across a write gap formed by a first pole and a second pole, and wherein a field extension next to the first pole extends further and creates a narrower side erase band than the field proximate to the second pole. The write current pulse width is controlled to set a magnetization length in the servo pattern created in the disk. Analog characteristic of a digital control signal in a variable width pulse generator is set to control a width of the write current pulse to control a magnetization length in the servo pattern created on the disk.

Abstract: A modem generally comprising an analog front end circuit, a hybrid circuit, and a variable impedance element. The hybrid circuit may be configured to couple the analog front end circuit to a transmission line. The variable impedance may be disposed within the analog front end circuit and connected to the hybrid circuit to trim an echo cancelling function of the hybrid circuit.

Abstract: A magneto-resistive (M-R) head has a read element with a servo sensing width as wide as a data track width and a data sensing width of less than one data track width. The two read sensing widths are achieved by using a single read element having a center electrical contact from the M-R read element that effectively reduces the sensing width of the read element. In a first embodiment, the servo sensing width comprises a first portion of the read element and the data sensing width comprises a second, smaller portion of the read element. In a second embodiment, the servo sensing width comprises the entire read element width and the data sensing width comprises a portion thereof. In yet another embodiment, abutting read elements are constructed to enable separate optimization of each sensing width. The wide servo sensing width permits use of a wide servo pattern having servo bursts as wide as a data track width.

Abstract: A servo system accurately detects and processes signals from servo patterns encoded on magnetic storage disks using weighted accumulation, for use in precisely positioning read/write heads with respect to tracks of data contained on the disks. After servo patterns are sensed by reading them from a disk, the resultant servo signals are processed by weighted accumulation circuitry to provide a position signal, which may be decoded to ascertain the positioning error of the read/write head and to apply any corrections that might be needed. In one embodiment, an amplitude position signal is generated by multiplying the servo signal by complementary quadrature weighting signals, then squaring each quadrature output signal, summing them, and taking the square root of the summed signal.