Skew compensation signal
The relative trajectory of a transducer head over bit-patterned media (BPM) may be skewed with respect to a down-track direction on the media (i.e., skew error). In order to resolve the skew error, the presently disclosed technology measures the skew error without adding additional patterning on the media. A detector circuit detects a sequential series of data bits on a storage media. The sequential series of data bits alternate between at least two tracks on the storage media. The sequential series of data bits are sent to a timing circuit, which sets a time stamp indicating when each data bit is received using, for example, a delay chain or a voltage ramp. A time elapsed between receiving a first data bit, a second data bit, and a third data bit is tracked. Transducer head skew is adjusted based on a signal containing the time elapsed between the bits.
1. A method comprising:
outputting a timing signal corresponding to transducer head skew including a first time elapsed between receiving first and second sequential data bits in a read-back signal; and
adjusting transducer head skew based on comparing the first time elapsed with a target time elapsed corresponding to an aligned reader head.
2. The method of claim 1 , wherein the first and second sequential data bits correspond to first and second patterned bits on two separate tracks on a media.
3. The method of claim 2 , wherein the media is a bit patterned media disc.
4. The method of claim 1 , wherein the timing signal further includes a second time elapsed between receiving the second sequential data bit and a third sequential data bit, wherein the first time elapsed and second time elapsed are different.
5. The method of claim 4 , wherein the first time elapsed corresponds to a time between reading a patterned bit on a first data track followed by a patterned bit on a second data track and the second time elapsed corresponds to a time between reading a patterned bit on the second data track followed by a patterned bit on the first data track.
6. The method of claim 4 , further comprising:
adjusting transducer head skew based on comparing the first time elapsed to the second time elapsed.
7. The method of claim 1 , wherein one or more additional data bits exist between the first and second sequential data bits.
8. The method of claim 1 , further comprising:
inputting the first data bit into a first stage of a delay chain having a known time delay between each stage of the delay chain; and
latching the output of the delay chain upon receipt of the second data bit at a data buffer, wherein a number of written data cells in the data buffer is a metric of the first time elapsed.
9. The method of claim 8 , wherein each stage of the delay chain corresponds to a time delay between writing two sequential cells of the data buffer.
10. The method of claim 1 , further comprising:
starting a voltage ramp upon receipt of the first data bit; and
stopping the voltage ramp upon receipt of the second data bit, wherein an output voltage of the voltage ramp is a metric of the first time elapsed.
11. A detector comprising:
a detector circuit configured to detect first and second sequential data bits in a read-back signal; and
a timing circuit configured to measure time elapsed between receiving the first and second sequential data bits, wherein the time elapsed corresponds to transducer head skew, wherein the timing circuit includes one or both of a delay chain and a voltage ramp.
12. The detector of claim 11 , wherein the first and second sequential data bits correspond to first and second patterned bits on two separate tracks on a media.
13. The detector of claim 11 , wherein the detector circuit is further configured to detect a second time elapsed between receiving the second sequential data bit and a third sequential data bit, wherein the first time elapsed and second time elapsed are different.
14. The detector of claim 13 , wherein the first time elapsed corresponds to a time between reading a patterned bit on a first data track followed by a patterned bit on a second data track and the second time elapsed corresponds to a time between reading a patterned bit on the second data track followed by a patterned bit on the first data track.
15. One or more non-transitory computer-readable storage media encoding computer-executable instructions for executing on a computer system a computer process, the computer process comprising:
outputting a timing signal corresponding to transducer head skew including a first time elapsed between receiving first and second sequential data bits in a read-back signal; and
adjusting transducer head skew based on comparing the first time elapsed with a target time elapsed corresponding to an aligned reader head.
16. The computer-readable storage media of claim 15 , wherein the first and second sequential data bits correspond to first and second patterned bits on two separate tracks on a media.
17. The computer-readable storage media of claim 15 , wherein the computer process further comprises:
inputting the first data bit into a first stage of a delay chain having a known time delay between each stage of the delay chain; and
latching the output of the delay chain upon receipt of the second data bit at a data buffer, wherein a number of written data cells in the data buffer is a metric of the first time elapsed.
18. The computer-readable storage media of claim 15 , wherein the computer process further comprises:
starting a voltage ramp upon receipt of the first data bit; and
stopping the voltage ramp upon receipt of the second data bit, wherein an output voltage of the voltage ramp is a metric of the first time elapsed.