Class of fixed partial response targets in a PRML sampled data detection channel

• US 6,249,398 B1
• Filed: 03/04/1998
• Issued: 06/19/2001
• Est. Priority Date: 03/04/1998
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation), Maxtor Corporation (Seagate Technology Holdings Plc)
• Original Assignee: Maxtor Corporation (Seagate Technology Holdings Plc)
• Inventors: Modlin, Cory, Fisher, Kevin, Fitzpatrick, Kelly K., Sayiner, Necip, Patapoutian, Ara, Sonntag, Jeffrey L.
• Primary Examiner(s): Hudspeth, David
• Assistant Examiner(s): DAVIDSON, DAN
• Application Number:
  US09/034,933
• Time in Patent Office: 1,203 Days
• Field of Search: 360/65, 360/46, 375/262, 375/263, 375/290, 375/340-341, 375/350, 714/794, 714/795
• US Class Current: 360/65
• CPC Class Codes: G11B 20/10009 Improvement or modification of read or write signals
• CPC Class Codes: G11B 20/10037 A/D conversion, D/A conversion, sampling, slicing and digital quantisation or adjusting parameters thereof
• CPC Class Codes: G11B 20/10055 using partial response filtering when writing the signal to the medium or reading it therefrom
• CPC Class Codes: G11B 20/10296 using the Viterbi algorithm
• CPC Class Codes: G11B 5/09 Digital recording

Abstract

A new class of fixed partial response targets are disclosed for use in a PRML magnetic medium read channel. The preferred embodiment exhibits an equalization response characterized by the polynomial 7+4*D−4*D²−5*D³−2*D⁴, where D represents the unit delay operator. This read channel target provides improved matching to the inherent magnetic channel over the known canonical class of targets (1−D)(1+D){circumflex over ( )}N, and thereby reduces equalization losses. The improved spectral matching reduces amplification of noise in the channel, thereby reducing bit-error-rates. The new class of targets also exhibits a spectral null at DC, reducing problems for offset cancellation circuitry and making the disk drive less sensitive to thermal asperities. It also exhibits a spectral depression rather than a spectral null at the Nyquist frequency, making quasi-catastrophic error sequences virtually impossible. The new class of target simplifies coding and allows RLL code ratios that approach unity, improving effective recording densities, while significantly reducing BER.

Claims

1. A magnetic recording and playback system including a moving magnetic data storage medium defining a data storage surface, a data transducer head positionable by head positioning means relative to a track formed on the data storage surface for storing user data in the form of magnetic flux transitions, the system further including a partial response, maximum likelihood data channel comprising:

an analog signal path coupled to the data transducer head and forming a read signal responsive to flux transitions during a read operation of the disk drive;

quantization means for quantizing samples of the read signal to form a series of samples;

an FIR filter for filtering the series of samples so as to implement a non-canonical fixed partial response target which has a spectral null at DC and a spectral depression at the Nyquist sampling frequency; and

a Viterbi detector having at least sixteen states and being arranged for maximum likelihood decoding of the filtered series of samples so as to form a series of detected bits.

2. A system according to claim 1 wherein the quantization means includes an analog to digital conversion means for converting the series of samples into a corresponding series of digital sample values;

and wherein the FIR filter means comprises an adaptive digital FIR filter for filtering the series of digital sample values, and the Viterbi detector is arranged to decode the filtered series of digital sample values.

3. A system according to claim 1 wherein the FIR filter implements a fourth-order non-canonical fixed partial response target.

4. A system according to claim 3 wherein the filter implements a fourth-order non-canonical fixed partial response target substantially equal to 7n+4nD−

4nD²−

5nD³−

2nD⁴, where n is a non-zero integer and D is the unit delay operator.

5. A system according to claim 3 wherein the filter implements a fourth-order non-canonical fixed partial response target substantially equal to 6n+5nD−

5nD²−

4nD³−

2nD⁴ where n is a non-zero integer and D is the unit delay operator.

6. A system according to claim 3 wherein the filter implements a fourth-order non-canonical fixed partial response target substantially equal to 5n+5nD−

5nD²−

4nD³−

1nD⁴ where n is a non-zero integer and D is the unit delay operator.

7. A system according to claim 3 wherein the filter implements a fourth-order non-canonical fixed partial response target substantially equal to 9n+3nD−

6nD²−

5nD³−

1nD⁴ where n is a non-zero integer and D is the unit delay operator.

8. A system according to claim 3 wherein the filter implements a fourth-order non-canonical fixed partial response target substantially equal to 7n+3nD−

5nD²−

4nD³−

1nD⁴ where n is a non-zero integer and D is the unit delay operator.

9. A system according to claim 1 where the non-canonical fixed partial response target has samples taken at peaks and zero crossings during playback of a 2T write current pattern.

10. A system according to claim 1 where the FIR filter implements a fourth-order non-canonical fixed partial response target that has samples taken at peaks and zero crossings during playback of a 2T write current pattern.

11. A magnetic read channel apparatus comprising:

a low-pass filter for filtering an analog read signal;

a sampling means for forming a series of digital sample values responsive to the filtered analog read signal;

an FIR filter for filtering the series of digital sample values; and

a Viterbi detector for determining a series of output bits responsive to the filtered series of digital sample values;

wherein the low-pass filter, the sampling means and the FIR filter together form an equalization circuit, and the equalization circuit has a non-canonical fixed partial response target which manifests a spectral null at DC and a spectral depression at the Nyquist sampling frequency.

12. A magnetic read channel apparatus according to claim 11 wherein the non-canonical fixed partial response target is a fourth order target described by a polynomial having a form of an+bnD+cnD²+dnD³+enD⁴, where a, b, c, d and e are integer coefficients, and n is a non-zero integer scale factor, and the sum a+b+c+d+e=0 and wherein b =−

c and a+d+e=0.

13. A magnetic read channel apparatus according to claim 12 wherein a−

b−

c+d+e=0.

14. A system according to claim 11 where the FIR filter implements a fourth-order non-canonical fixed partial response target that has samples taken at peaks and zero crossings during playback of a 2T write current pattern.

15. A magnetic read channel apparatus according to claim 14 wherein the Nyquist response is a−

b+c−

d+e=2w and b=−

c, d=−

b−

w, and e=−

a+b+w.

16. A method of equalizing a read signal in a partial response, maximum likelihood sampled data detection system of a magnetic recording and playback system that includes a moving data magnetic recording medium for storing and reading back data in the form of magnetic flux transitions on the medium via a data transducer assembly, the method comprising the steps of:

selecting a relative data density in a range of approximately 2.0 to 3.0 where the relative data density is defined as a pulse width measured at 50% amplitude of the natural response of the data transducer assembly, divided by a recording cell time;

recording user data on the magnetic recording medium at approximately the selected relative data density;

during a read operation, forming a read signal responsive to flux transitions on the magnetic recording medium;

sampling the read signal at substantially a selected sample rate to form a series of sampled data;

digitally filtering the sampled data, said filtering step including providing a fourth-order digital FIR filter configured to implement a non-canonical, at least fourth-order fixed partial response target response described by a polynomial of the form an+bnD+cnD²+dnD³+enD⁴, where a,b,c,d and e are integer coefficients, n is a non-zero integer scale factor and D is the unit delay operator, and wherein the target manifests a spectral null at DC; and

selecting the integer coefficients so that the target response exhibits a non-zero but attenuated response at the Nyquist frequency determined by the recording cell time.

17. A method according to claim 16 wherein the integer coefficients are a=7, b=4, c=−

4, d=−

5, and e=−

2.

18. A method according to claim 16 wherein the sampling step includes providing an A/D converter for converting the read signal to a series of digital samples and further comprising selecting the integer scale factor n in accordance with digital levels output by the A/D converter.

19. A method according to claim 16 wherein the scale factor n=1.

20. A method according to claim 16 wherein the said filtering step includes dynamically adapting the digital FIR filter to achieve the target polynomial response.

21. A method according to claim 16 wherein the coefficients a,b,c,d and e have the values listed in one row of the following table, respectively:

22. A method according to claim 21 wherein the scale factor n=1.

23. A method according to claim 16 wherein the integer coefficients are selected so as to provide a zero-crossing response to a 2T preamble sequence.

24. A magnetic read channel apparatus comprising:

a low-pass filter for filtering an analog read signal;

a sampling means for forming a series of digital sample values responsive to the filtered analog read signal;

an FIR filter for filtering the series of digital sample values; and

a Viterbi detector for determining a series of output bits responsive to the filtered series of digital sample values;

wherein the low-pass filter, the sampling means and the FIR filter together form an equalization circuit, and the equalization circuit has a non-canonical fixed partial response target substantially in accordance with 7n+4nD−

4nD²−

5nD<sup>3−

2</sup>nD⁴ where n is a non-zero integer and D is the unit delay operator.

25. A magnetic read channel apparatus comprising:

a low-pass filter for filtering an analog read signal;

a sampling means for forming a series of digital sample values responsive to the filtered analog read signal;

an FIR filter for filtering the series of digital sample values; and

a Viterbi detector for determining a series of output bits responsive to the filtered series of digital sample values;

wherein the low-pass filter, the sampling means and the FIR filter together form an equalization circuit, and the equalization circuit has a non-canonical fixed partial response target substantially in accordance with 6n+5nD−

5nD2−

4nD³−

2nD⁴ where n is a non-zero integer and D is the unit delay operator.

26. A magnetic read channel apparatus comprising:

a low-pass filter for filtering an analog read signal;

a sampling means for forming a series of digital sample values responsive to the filtered analog read signal;

an FIR filter for filtering the series of digital sample values; and

a Viterbi detector for determining a series of output bits responsive to the filtered series of digital sample values;

wherein the low-pass filter, the sampling means and the FIR filter together form an equalization circuit, and the equalization circuit has a fixed partial response target substantially in accordance with 5n+5nD−

5nD²−

4nD³−

1nD⁴ where n is a non-zero integer and D is the unit delay operator.

27. A magnetic read channel apparatus comprising:

a low-pass filter for filtering an analog read signal;

a sampling means for forming a series of digital sample values responsive to the filtered analog read signal;

an FIR filter for filtering the series of digital sample values; and

a Viterbi detector for determining a series of output bits responsive to the filtered series of digital sample values;

wherein the low-pass filter, the sampling means and the FIR filter together form an equalization circuit, and the equalization circuit has a non-canonical fixed partial response target substantially in accordance with 7n+3nD−

5nD²−

4nD³−

1nD⁴ where n is a non-zero integer and D is the unit delay operator.

28. A magnetic read channel apparatus comprising:

a low-pass filter for filtering an analog read signal;

a sampling means for forming a series of digital sample values responsive to the filtered analog read signal;

an FIR filter for filtering the series of digital sample values; and

a Viterbi detector for determining a series of output bits responsive to the filtered series of digital sample values;

wherein the low-pass filter, the sampling means and the FIR filter together form an equalization circuit, and the equalization circuit has a non-canonical fixed partial response target substantially in accordance with 9n+3nD−

6nD²−

5nD³−

1nD⁴ where n is a non-zero integer and D is the unit delay operator.