Granted Patent B1

US 8,201,066 · App. 12/058,540 · Granted Jun 12, 2012

Abstract

Claims (77)

1. A disk drive comprising:

a disk;

a head actuated over the disk to generate a read signal;

a sampling device operable to sample the read signal to generate a sequence of signal sample values; and

a trellis detector for detecting an estimated data sequence from the signal sample values, the trellis detector comprising a plurality of add/compare/select (ACS) circuits each corresponding to a state in a trellis, wherein each ACS circuit comprises:

a first error generator for generating a first error relative to a signal sample value and a first expected value corresponding to a first branch in the trellis;

a first adder for adjusting the first error in response to a first delta to generate a first adjusted error;

a first branch metric calculator for computing a first branch metric in response to the first adjusted error;

a first update circuit for updating the first delta in response to the first adjusted error;

a second error generator for generating a second error relative to the signal sample value and a second expected value corresponding to a second branch in the trellis;

a second adder for adjusting the second error in response to a second delta to generate a second adjusted error;

a second branch metric calculator for computing a second branch metric in response to the second adjusted error; and

a second update circuit for updating the second delta in response to the second adjusted error.

2. The disk drive as recited in claim 1 , wherein each ACS circuit is operable to:

add the first branch metric to a first path metric corresponding to a first state to generate a first candidate path;

add the second branch metric to a second path metric corresponding to a second state to generate a second candidate path; and

select between the first and second candidate paths.

3. The disk drive as recited in claim 2 , wherein each ACS circuit is further operable to update the delta if the corresponding candidate path is selected.

4. The disk drive as recited in claim 1 , wherein the first and second update circuits update the respective deltas according to:

Δ k =Δ k-1 +γ·e′ k

where:

Δ k is the delta;

e′ k is the adjusted error; and

γ is a gain.

5. The disk drive as recited in claim 1 , wherein the first delta corresponds to a first path through the trellis and the second delta corresponds to a second path through the trellis.

6. The disk drive as recited in claim 5 , wherein each ACS circuit is further operable to:

maintain N deltas, wherein N equals a number of possible paths through the trellis ending in the state corresponding to the ACS;

compute a branch metric for each of the N deltas;

compute a candidate path for each branch metric; and

select one of the candidate paths.

7. The disk drive as recited in claim 1 , wherein each delta comprises a DC offset in the signal sample values.

8. The disk drive as recited in claim 1 , wherein each delta comprises an intersymbol interference (isi) in the signal sample values.

9. The disk drive as recited in claim 8 , wherein the isi is generated according to:

isi k =a k +p k ·isi k-1 +q k ·isi k-2

where:

a k is a non-return to zero (NRZ) symbol corresponding to a k th state transition;

p k =p k-1 +η 1 ·e′ k-1 ·isi k-2 ;

q k =q k-1 +η 2 ·e′ k-1 ·isi k-3 ; and

η 1 and η 2 are gains.

10. The disk drive as recited in claim 9 , wherein each delta further comprises a DC offset in the signal sample values.

11. A method of operating a disk drive, the disk drive comprising a disk, a head actuated over the disk to generate a read signal, and a trellis detector for detecting an estimated data sequence from the read signal, the method comprising:

sampling the read signal to generate a sequence of signal sample values;

generating a first error relative to a signal sample value and a first expected value corresponding to a first branch in the trellis;

adjusting the first error in response to a first delta to generate a first adjusted error;

computing a first branch metric in response to the first adjusted error;

updating the first delta in response to the first adjusted error;

generating a second error relative to the signal sample value and a second expected value corresponding to a second branch in the trellis;

adjusting the second error in response to a second delta to generate a second adjusted error;

computing a second branch metric in response to the second adjusted error; and

updating the second delta in response to the second adjusted error.

12. The method as recited in claim 11 , further comprising:

adding the first branch metric to a first path metric corresponding to a first state to generate a first candidate path;

adding the second branch metric to a second path metric corresponding to a second state to generate a second candidate path; and

selecting between the first and second candidate paths.

13. The method as recited in claim 12 , wherein one of the first and second deltas is updated if the corresponding candidate path is selected.

14. The method as recited in claim 11 , wherein the first and second deltas are updated according to:

Δ k =Δ k-1 +γ·e′ k

where:

Δ k is the delta;

e′ k is the adjusted error; and

γ is a gain.

15. The method as recited in claim 11 , wherein the first delta corresponds to a first path through the trellis and the second delta corresponds to a second path through the trellis.

16. The method as recited in claim 15 , further comprising:

maintaining N deltas, wherein N equals a number of possible paths through the trellis ending in the state corresponding to the ACS;

computing a branch metric for each of the N deltas;

computing a candidate path for each branch metric; and

selecting one of the candidate paths.

17. The method as recited in claim 11 , wherein each delta comprises a DC offset in the signal sample values.

18. The method as recited in claim 11 , wherein each delta comprises an intersymbol interference (isi) in the signal sample values.

19. The method as recited in claim 18 , wherein the isi is generated according to:

isi k =a k +p k ·isi k-1 +q k ·isi k-2

where:

a k is a non-return to zero (NRZ) symbol corresponding to a k th state transition;

p k =p k-1 +η 1 ·e′ 2-1 ·isi k-2 ;

q k =q k-1 +η 2 ·e′ k-1 ·isi k-3 ; and

η 1 and η 2 are gains.

20. The method as recited in claim 19 , wherein each of the first and second deltas further comprises a DC offset in the signal sample values.

Assignments (6)