# US 11,908,502 B2 · Partial pulse pairing for improved read signal quality

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- Number: US 11,908,502 B2
- Document ID: US11908502B2
- Status: Granted
- Kind: B2
- Application number: 17/694,442
- Filed: 2022-03-14
- Published: 2023-09-14
- Granted: 2024-02-20
- Earliest claimed: 2022-03-14
- Assignees: Seagate Technology LLC
- Applicants: Seagate Technology LLC
- Inventors: Walter R. Eppler; Drew Michael Mader
- Web page: https://patentgrep.com/patent/US11908502B2

## CPC

- G11B 20/10018: {analog processing for digital recording or reproduction (G11B20/10037 - G11B20/10481 take precedence)}
- G11C 11/1673: {Reading or sensing circuits or methods}
- G11C 11/1675: {Writing or programming circuits or methods}
- G11C 11/1677: {Verifying circuits or methods}
- G11C 11/1693: {Timing circuits or methods}
- H03M 1/0636: {in the amplitude domain}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- G11C: STATIC STORES (semiconductor memory devices H10B)
- H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C)

## Abstract

A method for reducing noise in a read signal due attributable to read element asymmetry provides for transmitting a write signal through a write precompensation circuit that shifts rising edges and falling edges of each of pulse in the write signal by a select magnitude and in opposite directions. After the write signal is encoded on a media, a corresponding read signal is read, with a read element, from the media. The method further provides for transmitting the read signal through a magnetoresistive asymmetry compensation (MRAC) block that is tuned to correct second-order non-linearities characterized by a particular set of distortion signatures. The select magnitude of the waveform shift applied by the write precompensation circuit introduces a non-linear signal characteristic that combines with non-linear signal characteristics introduced by the read element to generate one of the particular distortion signatures that is correctable by the MRAC block.

## Claims

### Claim 1

A method of reducing distortion in a signal read from a storage device, the method comprising:
transmitting a write signal through a write precompensation circuit that shifts rising edges and falling edges of each pulse in the write signal by a select magnitude and in opposite directions;
writing the write signal output by the precompensation circuit to a storage media;
reading, with a read element, a read signal corresponding to the written write signal; and
transmitting the read signal through a magnetoresistive asymmetry compensation (MRAC) block, the MRAC block being tuned to correct second-order non-linearities characterized by a particular set of distortion signatures, wherein the select magnitude of the shift applied by the write precompensation circuit introduces a non-linear signal characteristic that combines with non-linear signal characteristics introduced by the read element to generate one of the particular distortion signatures that is correctable by the MRAC block.

### Claim 2 (depends on 1)

The method of claim 1, wherein the non-linear signal characteristics introduced by the read element include a first pair of echoes, and wherein the particular set of distortion signatures correctable by the MRAC block is characterized by a second pair of echoes with an amplitude ratio satisfying predefined criteria.

### Claim 3 (depends on 2)

The method of claim 2, wherein the non-linear signal characteristic introduced by the write precompensation block combines with one of the echoes introduced by the read element to modify an amplitude ratio of echoes in a Volterra model of a resulting signal input to the MRAC block, the modified amplitude ratio satisfying the predefined criteria such that the echoes are substantially removable by the MRAC block.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
performing a calibration to select the magnitude of the shift applied by the write precompensation circuit, the calibration providing for:
selectively incrementing the select magnitude of the shift through each value of a range of values;
for each value within the range, determining a difference between an output of the read element and a response of a reference system; and
selecting the magnitude of the shift to equal a select value within the range of values that minimizes the difference.

### Claim 5 (depends on 4)

The method of claim 4, further comprising:
measuring an amplitude ratio of a pair of echoes present in the read signal that has been transmitted through the MRAC block; and
selecting the range of values for the calibration based on the measured amplitude ratio.

### Claim 6 (depends on 1)

The method of claim 1, further comprising:
measuring an amplitude ratio of a pair of echoes in a Volterra model of a read signal, the echoes being introduced by the read element;
determining whether the measured amplitude radio is a ratio that is correctable by the MRAC block;
responsive to determining that the measured amplitude radio is not correctable by the MRAC block, performing a calibration to select the magnitude of the shift applied by the write precompensation circuit; and
configuring the write precompensation circuit to apply the shift.

### Claim 7 (depends on 1)

The method of claim 1, further comprising:
measuring non-linear signal characteristics of a read signal after the storage device has been deployed for use in-the-field; and
dynamically updating the select magnitude of the shift applied by the write precompensation block responsive to the measurement.

### Claim 8 (depends on 1)

The method of claim 1, wherein the MRAC block subtracts from the read signal a signal proportional to a square of the read signal.

### Claim 9

A read/write channel in a storage device comprising:
a write precompensation circuit that receives a write signal from a host device and that shifts rising edges and falling edges of each of pulse in the write signal by a select magnitude and in opposite directions; and
a magnetoresistive asymmetry compensation (MRAC) block that receives, from a read element, a read signal corresponding to the write signal, the MRAC block being tuned to correct second-order non-linearities characterized by a particular set of distortion signatures, wherein the select magnitude of the shift applied by the write precompensation circuit introduces a non-linear signal characteristic that combines with non-linear signal characteristics introduced by the read element to generate one of the particular distortion signatures that is correctable by the MRAC block.

### Claim 10 (depends on 9)

The read/write channel of claim 9, wherein the non-linear signal characteristics introduced by the read element include a first pair of echoes, and wherein the particular set of distortion signatures correctable by the MRAC block is characterized by a second pair of echoes with an amplitude ratio satisfying predefined criteria.

### Claim 11 (depends on 10)

The read/write channel of claim 10, wherein the non-linear signal characteristic introduced by the write precompensation block combines with one of the echoes introduced by the read element to modify an amplitude ratio of echoes in a Volterra model of a resulting signal input to the MRAC block, the modified amplitude ratio satisfying the predefined criteria such that the echoes are substantially removable by the MRAC block.

### Claim 12 (depends on 9)

The read/write channel of claim 9, wherein the select magnitude of the shifts is selected to minimize a difference between an output of the read element and a response of a reference system.

### Claim 13 (depends on 9)

The read/write channel of claim 9, wherein the set of distortion signatures correctable by the MRAC block are characterized by a set different of amplitude ratios associated with two echoes that appear in a Volterra model of the read signal and wherein the select magnitude of the shift applied by the write precompensation circuit introduces an amplitude shift in a preidentified one of the two echoes without substantially altering amplitude of a second echo of the two echoes.

### Claim 14 (depends on 9)

The read/write channel of claim 9, wherein the MRAC block subtracts from the read signal a signal proportional to a square of the read signal.

### Claim 15

One or more computer-readable storage media encoding computer-executable instructions for executing a computer process that reduces distortion in a signal read from a storage device, the computer process comprising:
transmitting a write signal through a write precompensation circuit that shifts rising edges and falling edges of each pulse in the write signal by a select magnitude and in opposite directions;
reading a read signal back from the media with a read element; and
transmitting the read signal through a magnetoresistive asymmetry compensation (MRAC) block, the MRAC block being tuned to correct second-order non-linearities characterized by a particular set of distortion signatures, wherein the select magnitude of the shift applied by the write precompensation circuit introduces a non-linear signal characteristic that combines with non-linear signal characteristics introduced by the read element to generate one of the particular distortion signatures that is correctable by the MRAC block.

### Claim 16 (depends on 15)

The one or more computer-readable storage media of claim 15, wherein the non-linear signal characteristics introduced by the read element include a first pair of echoes, and wherein the particular set of distortion signatures correctable by the MRAC block is characterized by a second pair of echoes with an amplitude ratio satisfying predefined criteria.

### Claim 17 (depends on 16)

The one or more computer-readable storage media of claim 16, wherein the non-linear signal characteristic introduced by the write precompensation block combines with one of the echoes introduced by the read element to modify an amplitude ratio of echoes that appear in a Volterra model of a resulting signal input to the MRAC block, the modified amplitude ratio satisfying the predefined criteria such that the echoes are substantially removable by the MRAC block.

### Claim 18 (depends on 16)

The one or more computer-readable storage media of claim 16, wherein the computer process further comprises:
measuring non-linear signal characteristics of a read signal after the storage device has been deployed for use in-the-field; and
dynamically updating the select magnitude of the shift applied by the write precompensation block responsive to the measurement.

### Claim 19 (depends on 15)

The one or more computer-readable storage media of claim 15, wherein the MRAC block subtracts from the read signal a signal proportional to a square of the read signal.

### Claim 20 (depends on 15)

The one or more computer-readable storage media of claim 15, wherein the non-linear signal characteristic introduced by the write precompensation block changes amplitude of an echo in the read signal such that resulting characteristics of the read signal more closely resemble a second-order system.