Wangtek

Frederick Electronics Corporation

Ronald E Tollum

John W Spaniol

Julius A Barthelme

The present invention discloses a method and an apparatus for the detection and correction of incorrectly digitized read data pulses corresponding to the pulses of an analog read signal generated from the reading of data from a magnetic storage tape. Detection of incorrectly digitized read data pulses is performed by delaying the signal to obtain a nominal signal and delaying the nominal signal to obtain a late signal. A recovered clock signal is used to synchronize and detect each of the early, nominal and late signals to obtain early, nominal and late synchronized data signals consisting of binary values. A predetermined number of binary values of each of the synchronized data signals is stored within first, second and third memory means. These binary values are then compared to determine whether any of the corresponding read data pulses were detected within an incorrect timing cell of the recovered clock. If the binary values within a preselected cell of each of the synchronized data signals are not the same, error correction is performed by comparing the contents of the memory means with error patterns empirically derived and selecting an appropriate binary value as the correct output of the data separator. If no error exists, then the binary value of a preselected cell is chosen as the correct data separator output.

Selective data synchronizer

A look ahead detector based on a delay line is used in a pulse amplitude qualifier circuit to qualify detected peaks in a system for the recovery of magnetically recorded digital information. The analog signal is delayed by one cell period to create a delayed replica which is applied to the peak detector. The difference between the analog signal and the delayed replica is applied to a hysteresis flip flop to create a qualifying signal based on a threshold value proportional to the analog signal to gate the peak detected in the delayed replica.

Peak detector with look ahead

Special tape drive read circuitry generally qualifies read voltage peaks by establishing a minimum amplitude for valid peaks in the read voltage signal so that noise is not interpreted as peaks, but does not require amplitude qualification during periods of dropout in the read voltage signal. Additional circuitry recognizes two of the data errors most common to GCR, and allows for these errors to be corrected. The first kind of error is the tri-bit error, in which 01110 is misinterpreted as 01000. The other kind of error is the low frequency error, in which 10010 is misinterpreted as 11000. Also, the type of error detected is used to adjust the read drive's hysteresis setting, to reduce future errors of the same type.

Magnetic recording system with pulse qualification and error correction

A teletypewriter line keyer with a switching current regulator responsive to a floating, loop current powered voltage comparator used as a loop current monitor. The line keyer, which may have positive and negative line current keying, uses a single current monitor to control positive and negative current regulators responsive to the positive and negative keying respectively. The switching regulators operate within a relatively narrow band centered around the nominal signaling current, with filtering being provided for ripple control. The circuit may also include a keying detector and open loop detector for system monitoring.

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Simi Valley, CA, United States of America

Ronald E Tollum