Decision directed timing recovery using multiphase detection
A sampled signal is processed by periodically sampling an input signal to obtain a set of samples. A first detection process is performed using the set of samples to obtain a first decision and a first error; the first detection process is associated with a first phase offset. A second detection process is performed using the set of samples to obtain a second decision and a second error; the second detection process is associated with a second phase offset. Either the first decision or the second decision is selected based at least in part on the first error and the second error.
1. A method for processing a sampled signal, comprising:
periodically sampling an input signal to obtain a set of samples;
using a processor to perform a first detection process using the set of samples to obtain a first decision and a first error, wherein the first detection process is associated with a first phase offset;
performing a second detection process using the set of samples to obtain a second decision and a second error, wherein the second detection process is associated with a second phase offset; and
selecting either the first decision or the second decision based at least in part on the first error and the second error, wherein selecting includes:
accumulating a first accumulated error based on a first plurality of consecutive errors associated with the first detection process;
accumulating a second accumulated error based on a second plurality of consecutive errors associated with the second detection process; and
using the first accumulated error and the second accumulated error in the selection.
2. The method of claim 1 , wherein accumulating the first accumulated error includes using a formula of
m
k
=
∑
i
=
0
k
α
i
·
d
k
-
i
2
,
wherein d j 2 is a squared distance associated with a time index j.
3. The method of claim 2 , wherein α is substantially equal to 0.75.
4. The method of claim 1 further comprising adjusting a sampling phase associated with the periodic sampling based at least in part on the selected decision.
5. The method of claim 1 further comprising:
performing a first timing error detection (TED) process on the first decision; and
performing a second TED process on the second decision, wherein performing the first TED process and the second TED process overlap in time.
6. A system for processing a sampled signal, comprising:
a sampler configured to periodically sample an input signal to obtain a set of samples;
a first detector configured to perform a first detection process using the set of samples to obtain a first decision and a first error, wherein the first detection process is associated with a first phase offset;
a second detector configured to perform a second detection process using the set of samples to obtain a second decision and a second error, wherein the second detection process is associated with a second phase offset; and
a selection block configured to select either the first decision or the second decision based at least in part on the first error and the second error, wherein the selection block is configured to select by:
accumulating a first accumulated error based on a first plurality of consecutive errors associated with the first detection process;
accumulating a second accumulated error based on a second plurality of consecutive errors associated with the second detection process; and
using the first accumulated error and the second accumulated error in the selection.
7. The system of claim 6 further comprising a control block configured to adjust a sampling phase associated with the periodic sampling based at least in part on the selected decision.
8. The system of claim 6 further comprising:
a first timing error detector configured to perform a first timing error detection (TED) process on the first decision; and
a second timing error detector configured to perform a second TED process on the second decision, wherein performing the first TED process and the second TED process overlap in time.
9. A computer program product for processing a sampled signal, the computer program product being embodied in a non-transitory computer readable storage medium and comprising computer instructions for:
periodically sampling an input signal to obtain a set of samples;
performing a first detection process using the set of samples to obtain a first decision and a first error, wherein the first detection process is associated with a first phase offset;
performing a second detection process using the set of samples to obtain a second decision and a second error, wherein the second detection process is associated with a second phase offset; and
selecting either the first decision or the second decision based at least in part on the first error and the second error, wherein the computer instructions for selecting include computer instructions for:
accumulating a first accumulated error based on a first plurality of consecutive errors associated with the first detection process;
accumulating a second accumulated error based on a second plurality of consecutive errors associated with the second detection process; and
using the first accumulated error and the second accumulated error in the selection.
10. The computer program product of claim 9 further comprising computer instructions for adjusting a sampling phase associated with the periodic sampling based at least in part on the selected decision.
11. The computer program product of claim 9 further comprising computer instructions for:
performing a first timing error detection (TED) process on the first decision; and
performing a second TED process on the second decision, wherein performing the first TED process and the second TED process overlap in time.
12. The method of claim 1 , wherein the first phase offset is a phase offset of 0.
13. The method of claim 1 , wherein the first phase offset and the second phase offset have the same magnitude but opposite signs.
14. The method of claim 1 , wherein periodically sampling includes accessing information stored in a disk drive system.
15. The method of claim 1 , wherein periodically sampling includes using an analog to digital converter (ADC).
16. The method of claim 1 , wherein performing the first detection process includes using a Dual Decision Feedback Equalizer (DDFE).
17. The method of claim 1 , wherein performing the first detection process includes interpolating the set of samples to obtain a first interpolated set of samples corresponding to the first phase offset.
18. The method of claim 1 , wherein selecting includes selecting a first plurality of consecutive decisions associated with the first detection process or a second plurality of consecutive decisions associated with the second detection process.
19. The system of claim 6 , wherein the selection block is configured to select by selecting a first plurality of consecutive decisions associated with the first detection process or a second plurality of consecutive decisions associated with the second detection process.
20. The computer program product of claim 9 , wherein the computer instructions for selecting include computer instructions for selecting a first plurality of consecutive decisions associated with the first detection process or a second plurality of consecutive decisions associated with the second detection process.