Zero Phase Start Estimation in Readback Signals
A data storage system identifies analog-to-digital conversion samples with amplitude below a certain threshold. Remaining samples are grouped according to phase into one or more quadrants. A multi-coordinate with overlapping quadrants is used to further differentiate sample points. The system then computes an average phase for zero phase start estimation.
Latest LSI Corporation Patents:
- DATA RATE AND PVT ADAPTATION WITH PROGRAMMABLE BIAS CONTROL IN A SERDES RECEIVER
- HOST-BASED DEVICE DRIVERS FOR ENHANCING OPERATIONS IN REDUNDANT ARRAY OF INDEPENDENT DISKS SYSTEMS
- Slice-Based Random Access Buffer for Data Interleaving
- Systems and Methods for Rank Independent Cyclic Data Encoding
- Systems and Methods for Self Test Circuit Security
The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/939,530, filed Feb. 13, 2014, which is incorporated herein by reference.
BACKGROUND OF THE INVENTIONData storage systems utilize readback signals to calibrate a read head before reading. Zero phase start is used to provide an initial timing error estimate in frontend digital phase-locked-loop (DPLL) timing loop. When the readback signal includes defects, phase estimation is less reliable. Defects are currently handled by lengthening the sample window or shifting the sample window. Lengthening or shifting the sample window introduces undesirable latency.
Consequently, it would be advantageous if an apparatus existed that is suitable for producing a reliable zero phase start estimation from initial readback signal samples, regardless of defects.
SUMMARY OF THE INVENTIONAccordingly, the present invention is directed to a novel method and apparatus for producing a reliable zero phase start estimation from initial readback signal samples, regardless of defects.
In one embodiment of the present invention, a data storage system identifies analog-to-digital conversion samples with amplitude below a certain threshold. Remaining samples are grouped according to phase into one or more quadrants. The system then computes an average phase for zero phase start estimation.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles.
The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which:
Reference will now be made in detail to the subject matter disclosed, which is illustrated in the accompanying drawings. The scope of the invention is limited only by the claims; numerous alternatives, modifications and equivalents are encompassed. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.
Referring to
In at least one embodiment, the processor 100 computes a sin term and a cos term for each 4 T in the readback signal. The sin term is computed according to the equation:
sin Termn=x[4n]−x[4n+2]
the cos term is computed according to the equation:
cos Termn=x[4n+1]−x[4n+4]
The processor 100 accumulates sin terms and cos terms for 16 T or 32 T. When the son terms and cos terms are accumulated, the processor 100 computes the input analog-to-digital conversion phase based on the accumulated terms.
Where the readback signal includes defects, the processor 100 determines a phase estimation by eliminating samples with sin terms and cos terms below a certain energy threshold. In at least one embodiment of the present invention, the processor 100 filters samples where the sin term squared plus the cos term squared is below a desired threshold. Furthermore, the processor 100 weighs samples based on accumulated sample phase location in a coordinate system; defective samples tend toward a random phase distribution.
Referring to
Referring to
Referring to
Referring to
Where the first sin terms axis 502 and first cos terms axis 500 overlap with the second sin term axis 506 and second cos term axis 504, the combined coordinate system defines eight regions 508, 510, 512, 514, 516, 518, 520, 522. Each region 508, 510, 512, 514, 516, 518, 520, 522 defines an overlap portion of the two underlying coordinate systems. While the regions 508, 510, 512, 514, 516, 518, 520, 522 in
In at least one embodiment of the present invention, each calculated sin term and cos term of each readback signal point falls into one of the regions (in this case quadrants) defined by each coordinate system. Generally, valid readback signal points 526, 528, 530, 532 will fall into one quadrant of either the first coordinate system or the second coordinate system. Defective readback signal points 534 will be distributed randomly. In the present example, all of the valid readback signal points 526, 528, 530, 532 appear in the first quadrant of the first coordinate system. Furthermore, defective readback signal points 534 tend to have lower amplitude than valid readback signal points 526, 528, 530, 532. Therefore, in at least one embodiment of the present invention, a threshold amplitude 524 defines a cut-off below which readback signal points are considered defective. Once one of the quadrants includes a predetermined number of valid readback signal points 526, 528, 530, 532, the final input phase is estimated.
Referring to
Referring to
It is believed that the present invention and many of its attendant advantages will be understood by the foregoing description of embodiments of the present invention, and it will be apparent that various changes may be made in the form, construction, and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof, it is the intention of the following claims to encompass and include such changes.
Claims
1. A computer apparatus comprising:
- a processor;
- memory connected to the processor; and
- computer executable program code configured to execute on the processor, wherein the computer executable program code is configured to: receive a plurality of readback signal samples; determine a sin term for each readback signal sample; determine a cos term for each readback signal sample; organize the readback signal samples according to the corresponding sin terms and cos terms; and compute an input phase based on the organized readback signal samples.
2. The computer apparatus of claim 1, wherein organizing the readback signal samples comprises:
- defining a first coordinate system, a first axis of the first coordinate system corresponding to sin function and a second axis of the first coordinate system corresponding to a cos function; and
- placing each readback signal sample in the first coordinate system.
3. The computer apparatus of claim 2, wherein the computer executable program code is further configured to:
- maintain a region counter corresponding to each of a plurality of regions in the first coordinate system;
- increment a corresponding region counter each time a readback signal sample is organized into the corresponding region; and
- identify when one of the plurality of regions includes a threshold number of readback signal samples.
4. The computer apparatus of claim 2, wherein organizing the readback signal samples further comprises:
- defining a second coordinate system, a first axis of the second coordinate system corresponding to sin function and a second axis of the second coordinate system corresponding to a cos function, the second coordinate system being offset from the first coordinate system by a predetermined angle; and
- placing each readback signal sample in the second coordinate system.
5. The computer apparatus of claim 4, wherein the computer executable program code is further configured to:
- maintain a region counter corresponding to each of a plurality of regions in the second coordinate system;
- increment a corresponding region counter each time a readback signal sample is organized into the corresponding region; and
- identify when one of the plurality of regions includes a threshold number of readback signal samples.
6. The computer apparatus of claim 4, wherein each readback signal sample comprises a 4 T signal and each of the first coordinate system and second coordinate system comprises four quadrants.
7. The computer apparatus of claim 1, wherein the computer executable program code is further configured to:
- define an amplitude threshold; and
- exclude any readback signal samples that fall below the amplitude threshold from the computation of input phase.
8. A method for estimating a readback signal phase comprising:
- receiving a plurality of readback signal samples;
- determining a sin term for each readback signal sample;
- determining a cos term for each readback signal sample;
- organizing the readback signal samples according to the corresponding sin terms and cos terms; and
- computing an input phase based on the organized readback signal samples.
9. The method of claim 8, wherein organizing the readback signal samples comprises:
- defining a first coordinate system, a first axis of the first coordinate system corresponding to sin function and a second axis of the first coordinate system corresponding to a cos function; and
- placing each readback signal sample in the first coordinate system.
10. The method of claim 9, further comprising:
- maintaining a region counter corresponding to each of a plurality of regions in the first coordinate system;
- incrementing a corresponding region counter each time a readback signal sample is organized into the corresponding region; and
- identifying when one of the plurality of regions includes a threshold number of readback signal samples.
11. The method of claim 9, wherein organizing the readback signal samples further comprises:
- defining a second coordinate system, a first axis of the second coordinate system corresponding to sin function and a second axis of the second coordinate system corresponding to a cos function, the second coordinate system being offset from the first coordinate system by a predetermined angle; and
- placing each readback signal sample in the second coordinate system.
12. The method of claim 11, further comprising:
- maintaining a region counter corresponding to each of a plurality of regions in the second coordinate system;
- incrementing a corresponding region counter each time a readback signal sample is organized into the corresponding region; and
- identifying when one of the plurality of regions includes a threshold number of readback signal samples.
13. The method of claim 8, further comprising:
- defining an amplitude threshold; and
- excluding any readback signal samples that fall below the amplitude threshold from the computation of input phase.
14. A data storage system comprising:
- a processor;
- memory connected to the processor;
- a data storage element connected to the processor; and
- computer executable program code configured to execute on the processor,
- wherein the computer executable program code is configured to: receive a plurality of readback signal samples from the data storage element; determine a sin term for each readback signal sample; determine a cos term for each readback signal sample; organize the readback signal samples according to the corresponding sin terms and cos terms; and compute an input phase based on the organized readback signal samples.
15. The data storage system of claim 14, wherein organizing the readback signal samples comprises:
- defining a first coordinate system, a first axis of the first coordinate system corresponding to sin function and a second axis of the first coordinate system corresponding to a cos function; and
- placing each readback signal sample in the first coordinate system.
16. The data storage system of claim 15, wherein the computer executable program code is further configured to:
- maintain a region counter corresponding to each of a plurality of regions in the first coordinate system;
- increment a corresponding region counter each time a readback signal sample is organized into the corresponding region; and
- identify when one of the plurality of regions includes a threshold number of readback signal samples.
17. The data storage system of claim 15, wherein organizing the readback signal samples further comprises:
- defining a second coordinate system, a first axis of the second coordinate system corresponding to sin function and a second axis of the second coordinate system corresponding to a cos function, the second coordinate system being offset from the first coordinate system by a predetermined angle; and
- placing each readback signal sample in the second coordinate system.
18. The data storage system of claim 17, wherein the computer executable program code is further configured to:
- maintain a region counter corresponding to each of a plurality of regions in the second coordinate system;
- increment a corresponding region counter each time a readback signal sample is organized into the corresponding region; and
- identify when one of the plurality of regions includes a threshold number of readback signal samples.
19. The data storage system of claim 17, wherein each readback signal sample comprises a 4 T signal and each of the first coordinate system and second coordinate system comprises four quadrants.
20. The data storage system of claim 14, wherein the computer executable program code is further configured to:
- define an amplitude threshold; and
- exclude any readback signal samples that fall below the amplitude threshold from the computation of input phase.
Type: Application
Filed: Mar 5, 2014
Publication Date: Aug 13, 2015
Applicant: LSI Corporation (San Jose, CA)
Inventors: Xuebin Wu (San Jose, CA), Shaohua Yang (San Jose, CA), Zhi Bin Li (Shanghai), Haitao Xia (San Jose, CA)
Application Number: 14/197,748