Sperry Corporation

Digital Equipment Corporation

Chao S Chi

Peter T McLean

John W Craig

Norman A Field

A quaternary saturated digital magnetic recording system for enhancing information entropy provides an effective bit density increase of 100% or more over the MFM code. In the simplest implementation, groups of two input binary bits are mapped into one data cell, preferably into four combinations of long or short breaks and positive or negative polarity, with the break optionally centralized within the data cell for self-clocking. A system for reproducing the recorded information provides a peak detector, responsive to the recorded signal, coupled to pulse polarity and break width detector circuitry, with an internally synchronized clock, for remapping the recorded data into binary format.

Triplex digital magnetic recording and reproducing system

An automatically adjustable equalizer for modifying the spectral contour of digital, analog, and magnetically recorded signals. A temperature sensor-controlled switching circuit automatically adjusts the delay and forward gain parameters of the equalizer so as to optimize the equalization contour, in discrete ranges, over a wide range of temperatures, pressures or other physical processes or conditions.

Adjustable equalizer

The Controlled Return to A.C. (CRA) magnetic recording and reproducing system applies a high frequency erase signal continuously to the write head except at the detents. At the detents polarity controlled interruptions of the high frequency erase signal are embedded therein. A positive interruption, a negative interruption and the absence of an interruption provides a ternary recording capability at the detent. The high frequency erase signal is controlled in phase to provide polarity coherent interruptions. A CRA cell includes two controlled interruptions providing a mapping of three binary digits into two CRA digits. The controlled interruption results in an opposite polarity pulse pair upon readback.

Controlled return to A.C. digital magnetic and reproducing system

A thin film magnetic read/write transducer has a substrate of magnetic material forming a pair of disparate pole pieces. Arranged adjacent a movable magnetic medium, the disparate pole pieces are constructed so that the leading pole piece has a greater distal surface area than the trailing pole piece. In an alternative arrangement the leading pole piece distal surface is disposed a greater distance from the medium than the trailing pole piece. In yet another arrangement the trailing pole piece distal surface is disposed at an acute angle to the medium, and the leading pole piece surface may be at a lesser angle or parallel to the medium. The disparate pole pieces, so constructed and arranged, introduce compensating non-linearities to the writing magnetic field to substantially counteract the non-linear properties of the medium and of the recording process.

Thin film magnetic head having disparate poles for pulse asymmetry

A detector for determining whether the time duration between a positive and a negative peak of a waveform is greater or less than a predetermined time interval comprises a delay line for delaying the waveform by the predetermined time interval. A peak detector of a first polarity for detecting the first occurring peak of the waveform is responsive to the delayed waveform to provide a signal upon the occurrence of the first occurring peak thereof. A peak detector of a second polarity for detecting the second occurring peak of the waveform is responsive to the undelayed waveform for providing a signal upon the occurrence of the second occurring peak thereof. A time sequence comparator provides a first output indication when the signal from the first peak detector occurs prior to the signal from the second peak detector and a second output indication when the signal from the second peak detector occurs prior to the signal from the first peak detector.

Precision time duration detector

The transducer for perpendicular magnetic recording comprises a core of high permeability material having a recording pole and a flux return pole spaced apart and connected by an intermediate member forming an inverted generally U-shaped core. The cross sectional area of the flux return pole is substantially greater than that of the recording pole. Current applied to a coil wound around the recording pole generates flux for recording on the magnetic medium. A similarly shaped second core may be disposed on the opposite side of the medium with respect to the first core for providing a flux return path for the first core. A sub-core of high permeability material mounted on the flux return pole forms a gap with the recording pole to provide a ring-type head for data recovery. Current applied to a coil wound on the sub-core saturates the sub-core to render it ineffective during perpendicular magnetic writing. During reading the sub-core winding is de-energized, transforming the perpendicular magnetic recording head into a ring-type reading head. An alternative reading embodiment utilizes magneto-resistive elements disposed between the recording pole and the flux return pole.

Transducer for perpendicular magnetic recording

In a feedback control system wherein data pulses also establish timing coordination between the data and the processing devices, two delay circuits are provided to extract the synchronized clock pulses from the coded incoming signal. This enables relative digital decoding and ensures a precise data transfer to a computer interface. One of the delay circuits enables a data reconditioner circuit to buffer the data and eliminates data peak shifting. The reconditioned data is provided to a coincident circuit which selectively transfers the data to a computer interface and to a phase difference detector. The other delay circuit provides to the phase difference detector a second input corresponding in time to the coded incoming data pulses. The detector's output generates a DC error voltage which synchronizes a voltage controlled oscillator (VCO). The outputs of the VCO are clock pulses in phase with the coded incoming signals. The feedback control system is capable of operating over a range of frequencies without effecting the margin for peak shifting.

Phase lock loop with delay circuits for relative digital decoding over a

A zero-crossing detecting circuit where the input signal is applied to positive and negative threshold circuits. Each threshold circuit is connected to the input of a respective one-shot circuit which responds to the beginning edge of each output signal from its threshold circuit. The output pulses of both one-shots are applied to a NOR circuit which thereby responds to the beginning edges but not the trailing edges of the signals from the threshold circuits. Accordingly, variations in the trailing edges of the signals from the threshold circuits due to hysteresis or varying propogation times do not effect the circuit's output.

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Shrewsbury, MA, United States of America

Chao S Chi