Systems and methods for format efficient timing recovery in a read channel
Various embodiments of the present invention provide systems, methods and media formats for processing user data derived from a storage medium. As an example, a system is described that includes a storage medium with a series of data. The series of data includes a servo data and a user data region. The user data region includes a first synchronization pattern and a second synchronization pattern located a distance from the first synchronization pattern. A storage buffer is provided that is operable to receive at least a portion of the series of data. A retiming circuit calculates an initial phase offset and frequency offset for a defined bit within the storage buffer using a first location of the first synchronization pattern and a second location of the second synchronization pattern. An error correction loop circuit re-samples the series of data from the storage buffer based at least in part on the initial phase offset and a frequency offset.
1. A bit density efficient system for accurately processing user data derived from a storage medium, the system comprising:
a storage medium including a series of data, wherein the series of data includes a user data region, and wherein the user data region includes a first synchronization pattern and a second synchronization pattern located a distance from the first synchronization pattern;
a storage buffer, wherein the storage buffer is operable to receive at least a portion of the series of data;
a retiming circuit, wherein the retiming circuit is operable to calculate an initial phase offset and frequency offset for a defined bit within the storage buffer using a first location of the first synchronization pattern and a second location of the second synchronization pattern, and wherein the retiming circuit includes:
a first location calculation circuit, wherein the first location calculation circuit is operable to determine a first location corresponding to the first synchronization pattern;
a second location calculation circuit, wherein the second location calculation circuit is operable to determine a second location corresponding to the second synchronization pattern;
a frequency offset calculation circuit, wherein the frequency offset calculation circuit is operable to calculate a frequency offset based at least in part on the first location and the second location; and
an initial phase offset circuit, wherein the initial phase offset circuit is operable to calculate an initial phase offset based at least in part on the frequency offset; and
an error correction loop circuit, wherein the error correction loop circuit is operable to re-sample the series of data from the storage buffer based at least in part on the initial phase offset and a frequency offset.
2. The system of claim 1 , wherein calculating the frequency offset is done in accordance with the following equation:
the
frequency
offset
=
the
second
location
-
the
first
location
the
distance
-
1.
3. The system of claim 2 , wherein calculating the initial phase offset is done in accordance with the following equation:
the initial phase offset=the first location−(bit periods)the frequency offset,
wherein the bit periods corresponds to the number of bit periods from the first location to which the initial phase offset corresponds.
4. The system of claim 1 , wherein the first location calculation circuit comprises:
a synchronization detector circuit, wherein the synchronization detector circuit is operable to detect the first synchronization pattern; and
a location calculation circuit, wherein the location calculation circuit calculates a location of where the first synchronization pattern was detected by the synchronization detector circuit.
5. The system of claim 4 , wherein the first location calculation circuit further comprises:
a T/2 interpolation circuit, wherein the T/2 interpolation circuit provides at least an additional point from which the location of where the first synchronization pattern was detected can be found.
6. The system of claim 5 , wherein the location of where the first synchronization pattern was detected is within one quarter sampling period of the actual location of the first synchronization pattern.
7. The system of claim 1 , wherein the retiming circuit comprises:
a window signal circuit, wherein the window signal circuit is operable to identify a first window during which the first synchronization pattern is expected within the series of data, and wherein the window signal circuit is operable to identify a second window during which the second synchronization pattern is expected within the series of data.
8. The system of claim 1 , wherein the error correction loop circuit comprises:
a digital phase lock loop circuit, wherein the digital phase lock loop circuit receives the initial phase offset and the frequency offset, and provides a bit period by bit period updated phase shift output; and
an interpolator circuit, wherein the interpolator circuit interpolates the series of data accessed from the storage buffer.
9. The system of claim 8 , wherein the series of data accessed from the storage buffer is multiplied by a gain correction factor prior to being interpolated by the interpolator circuit.
10. The system of claim 8 , wherein the error correction loop circuit further comprises:
a data detector circuit, wherein a detection algorithm is applied to an output derived from the interpolator circuit to yield a data output, and wherein the bit period by bit period updated phase shift output provided by the digital phase lock loop circuit is based at least in part on the data output.
11. A method for processing user data derived from a storage medium, the method comprising:
providing a storage medium including a series of data, wherein the series of data includes a user data region, and wherein the user data region includes a first synchronization pattern and a second synchronization pattern located a distance from the first synchronization pattern;
sampling data from the storage medium and storing the resulting series of data samples to a storage buffer;
determining a first location of the first synchronization pattern;
determining a second location of the second synchronization pattern;
calculating a frequency offset and an initial phase offset based at least in part on the first location and the second location, wherein calculating the frequency offset is done in accordance with the following equation:
the
frequency
offset
=
the
second
location
-
the
first
location
the
distance
-
1
;
and
interpolating at least a portion of the series of data from the storage buffer based at least in part on the frequency offset and the initial phase offset.
12. The method of claim 11 , wherein determining the first location of the first synchronization pattern includes:
detecting the first synchronization pattern in the series of data and asserting a first synchronization pattern found signal; and
determining a number of bit periods from a defined point until assertion of the first synchronization pattern found signal.
13. The method of claim 11 , wherein the data is sampled at a period T to yield T samples, and wherein determining the first location of the first synchronization pattern further includes:
interpolating the series of data using a T/2 interpolator circuit to yield T/2 samples;
determining which of a T sample or T/2 sample exhibits a maximum within a first synchronization pattern window; and
assigning a location of the determined T sample or T/2 sample as the first location.
14. The method of claim 13 , wherein determining the second location of the second synchronization pattern includes:
detecting the second synchronization pattern in the series of data and asserting a second synchronization pattern found signal;
determining a number of bit periods from the defined point until assertion of the second synchronization pattern found signal.
15. The method of claim 14 , wherein determining the second location of the second synchronization pattern further includes:
interpolating the series of data using a T/2 interpolator circuit to yield T/2 samples;
determining which of a T sample or T/2 sample exhibits a maximum within a second synchronization pattern window; and
assigning a location of the determined T sample or T/2 sample as the second location.
16. The method of claim 11 , wherein calculating the initial phase offset is done in accordance with the following equation:
the initial phase offset=the first location−(bit periods)the frequency offset,
wherein the bit periods corresponds to the number of bit periods from the first location to which the initial phase offset corresponds.
17. The method of claim 16 , wherein the bit periods correspond to a number of bit periods between the beginning of the user data region and the first location.
18. A storage system, the storage system comprising:
a storage medium including a series of data, wherein the series of data includes a user data region, and wherein the user data region includes a first synchronization pattern and a second synchronization pattern located a distance from the first synchronization pattern;
a read/write head assembly disposed in relation to the storage medium;
a read channel circuit, wherein the read channel circuit is operable to receive an analog input derived from the read/write head assembly that corresponds to the series of data, and wherein the read channel circuit includes:
a storage buffer, wherein the storage buffer is operable to receive at least a portion of the series of data;
a retiming circuit, wherein the retiming circuit is operable to calculate an initial phase and frequency offset for a defined bit within the storage buffer using a first location of the first synchronization pattern and a second location of the second synchronization pattern, and wherein the retiming circuit includes:
a first location calculation circuit, wherein the first location calculation circuit is operable to determine a first location corresponding to the first synchronization pattern;
a second location calculation circuit, wherein the second location calculation circuit is operable to determine a second location corresponding to the second synchronization pattern;
a frequency offset calculation circuit, wherein the frequency offset calculation circuit is operable to calculate a frequency offset based at least in part on the first location and the second location; and
an initial phase offset circuit, wherein the initial phase offset circuit is operable to calculate an initial phase offset based at least in part on the frequency offset; and
an error correction loop circuit, wherein the error correction loop circuit is operable to interpolate the series of data from the storage buffer based at least in part on the initial phase offset and a frequency offset.
19. The storage system of claim 18 , wherein the first location calculation circuit comprises:
a synchronization detector circuit, wherein the synchronization detector circuit is operable to detect the first synchronization pattern; and
a location calculation circuit, wherein the location calculation circuit calculates a location of where the first synchronization pattern was detected by the synchronization detector circuit.
20. The storage system of claim 19 , wherein the first location calculation circuit further comprises:
a T/2 interpolation circuit, wherein the T/2 interpolation circuit provides at least an additional point from which the location of where the first synchronization pattern was detected can be found.