# US 6,115,198 A · PR4 sampled amplitude read channel for detecting user data and embedded servo data > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,115,198 A - Document ID: US6115198A - Status: Granted - Kind: A - Application number: 08/960,471 - Filed: 1997-10-29 - Granted: 2000-09-05 - Earliest claimed: 1997-10-29 - Assignees: Cirrus Logic, Inc. - Inventors: David E. Reed; William G. Bliss - Web page: https://patentgrep.com/patent/US6115198A ## CPC - G11B 5/5965: {Embedded servo format (G11B5/59655 takes precedence)} - G11B 20/10074: {EPR4, i.e. extended partial response class 4, polynomial (1-D) *(1+D)2} - G11B 20/10175: {PR4, PR(1,0,-1), i.e. partial response class 4, polynomial (1+D)(1-D)=(1-D2)} - G11B 20/10277: {the demodulation process being specifically adapted to partial response channels, e.g. PRML decoding} - G11B 2020/10916: {Seeking data on the record carrier for preparing an access to a specific address} - G11B 2020/1267: {Address data} - G11B 2020/1281: {Servo information} - G11B 2220/2516: Hard disks - 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) ## Abstract A partial response class-IV (PR4) sampled amplitude read channel is disclosed for detecting user data and embedded servo data. The detected servo data is encoded using a novel servo code capable of accurately decoding detected codewords representing servo track address during seek operations, even when the recording head flies between two adjacent tracks, and capable of correcting errors in the detected codedwords caused by noise in the read signal, such as inter-symbol interference. In one embodiment, the servo code corrects certain minimum distance error events, such as a bit shift error event, associated with a trellis type sequence detector. To achieve the equivalent effect of a conventional Gray code, the codewords are arranged such that adjacent track addresses differ by a number of bits relative to the minimum distance error events corrected. In this manner, when the recording head spans two adjacent tracks during a seek operation, the ambiguity in the detected codeword will be resolved in favor of one of the adjacent track addresses. To further increase performance, the servo data PR4 sample values are converted into an EPR4 response and detected with a sliding threshold detector. This modification provides the same performance gain as a PR4 sequence detector matched to a d=1 constraint, but at less cost. One of the PR4 sliding threshold detectors for detecting user data can be advantageously shared to detect the servo data-the only additional hardware required is a 1+D filter for converting the PR4 samples of the servo data to EPR4 samples. ## Claims ### Claim 1 A sampled amplitude read channel for reading user data and servo data recorded on a disk storage medium by detecting an estimated data sequence from discrete time sample values generated by sampling an analog read signal emanating from a read head positioned over the disk storage medium, comprising: (a) a sampling device for sampling the analog read signal to generate the discrete-time sample values; (b) a discrete-time equalizer for equalizing the discrete-time sample values into PR4 sample values; (c) a conversion filter for converting the PR4 sample values into EPR4 sample values; (d) a first sliding threshold detector for detecting the servo data from the EPR4 sample values; and (e) a servo decoder for decoding the servo data into a servo track address. ### Claim 2 (depends on 1) The sampled amplitude read channel as recited in claim 1, further comprising a discrete-time timing recovery circuit, responsive to the PR4 sample values, for generating synchronous sample values. ### Claim 3 (depends on 2) The sampled amplitude read channel as recited in claim 2, further comprising a discrete-time sequence detector for detecting the estimated data sequence from the synchronous sample values. ### Claim 4 (depends on 3) The sampled amplitude read channel as recited in claim 3, wherein the discrete-time sequence detector comprises: (a) the first sliding threshold detector for detecting a first and second interleave of the servo data and a first interleave of the user data; and (b) a second sliding threshold detector for detecting a second interleave of the user data. ### Claim 5 (depends on 1) The servo decoder as recited in claim 1, wherein the servo decoder corrects a single bit shift error event in the detected servo data. ### Claim 6 (depends on 1) The servo decoder as recited in claim 1, wherein the servo track address comprises a d=1 run-length constraint. ### Claim 7 (depends on 1) The servo decoder as recited in claim 1, wherein the conversion filter is a 1+D filter. ### Claim 8 A sampled amplitude read channel for reading user data and servo data recorded on a disk storage medium by detecting an estimated data sequence from discrete time sample values generated by sampling an analog read signal emanating from a read head positioned over the disk storage medium, comprising: (a) a sampling device for sampling the analog read signal to generate the discrete-time sample values; (b) a discrete-time equalizer for equalizing the discrete-time sample values into first partial response sample values; (c) a conversion filter for converting the first partial response sample values into second partial response sample values; (d) a servo data detector for detecting the servo data from the second partial response sample values; and (e) a servo decoder for decoding the servo data in to a servo track address. ### Claim 9 (depends on 8) The sampled amplitude read channel as recited in claim 8, further comprising a discrete-time timing recovery circuit, responsive to the first partial response sample values, for generating synchronous sample values. ### Claim 10 (depends on 9) The sampled amplitude read channel as recited in claim 9, further comprising a discrete-time sequence detector for detecting the estimated data sequence from the synchronous sample values. ### Claim 11 (depends on 10) The sampled amplitude read channel as recited in claim 10, wherein the discrete-time sequence detector comprises: (a) a first sliding threshold detector for detecting a first and second interleave of the servo data and a first interleave of the user data; and (b) a second sliding threshold detector for detecting a second interleave of the user data. ### Claim 12 (depends on 8) The servo decoder as recited in claim 8, wherein the servo decoder corrects a single bit shift error event in the detected servo data. ### Claim 13 (depends on 8) The servo decoder as recited in claim 8, wherein the servo track address comprises a d=1 run-length constraint. ### Claim 14 (depends on 8) The servo decoder as recited in claim 8, wherein the conversion filter is a 1+D filter. ### Claim 15 (depends on 8) The servo decoder as recited in claim 8, wherein: (a) the first partial response sample values are PR4 sample values; and (b) the second partial response sample values are EPR4 sample values. ### Claim 16 A sampled amplitude read channel for reading user data and servo data recorded on a disk storage medium by detecting an estimated data sequence from discrete time sample values generated by sampling an analog read signal emanating from a read head positioned over the disk storage medium, comprising: (a) a sampling device for sampling the analog read signal to generate the discrete-time sample values; (b) a discrete-time equalizer for equalizing the discrete-time sample values into partial response sample values; (c) a discrete-time sequence detector comprising a first sliding threshold detector for detecting a first and second interleave of the servo data and a first interleave of the user data, and a second sliding threshold detector for detecting a second interleave of the user data; and (d) a servo decoder for decoding the servo data into a servo track address. ### Claim 17 (depends on 16) The servo decoder as recited in claim 16, wherein the servo decoder corrects a single bit shift error event in the detected servo data. ### Claim 18 (depends on 16) The servo decoder as recited in claim 16, wherein the servo track address comprises a d=1 run-length constraint.