Circuit and method for determining the phase difference between a sample clock and a sample signal by linear approximation

• US 6,366,225 B1
• Filed: 02/14/2000
• Issued: 04/02/2002
• Est. Priority Date: 02/14/2000
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Ozdemir, Hakan
• Primary Examiner(s): JEAN PIERRE, PEGUY
• Application Number:
  US09/503,929
• Time in Patent Office: 778 Days
• Field of Search: 341/111, 341/155, 375/345, 375/327, 375/329, 375/341
• US Class Current: 341/111
• 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 20/10296 using the Viterbi algorithm
• CPC Class Codes: G11B 20/1403 characterised by the use of two levels
• CPC Class Codes: H03L 7/091 the phase or frequency detector using a sampling device H03L7/087 takes precedence
• CPC Class Codes: H04L 2007/047 using a sine signal or unmodulated carrier
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04L 7/0054 Detection of the synchronisation error by features other than the received signal transition by means of signal transition H04L7/033

Abstract

A phase-calculation circuit includes a buffer, an approximation circuit, and an interpolator. The buffer receives and stores first and second samples of a periodic signal having a peak amplitude. The approximation circuit linearly approximates a portion of the periodic signal, and calculates the relative phase of one of the samples within the signal portion. The interpolator then calculates the absolute phase of the one sample with respect to a predetermined point of the signal using the relative phase of the sample within the signal portion and the values of the first and second samples. Such a circuit can be used to decrease the alignment-acquisition time of a digital timing-recovery loop, and thus allows a shortening of the preamble and a corresponding increase in the data-storage density of a disk. In one application, the circuit determines an initial phase difference between a disk-drive read signal and a read-signal sample clock. The digital timing-recovery circuit uses this phase difference to provide an initial coarse alignment between the read signal and the sample clock. By providing an initial coarse alignment, the recovery circuit reduces the overall alignment-acquisition time.

Claims

1. A circuit, comprising:

a buffer operable to receive and store first and second samples of a periodic signal having a peak amplitude and a zero crossing;

an approximation circuit coupled to the buffer and operable to approximate a portion of the periodic signal as a straight line and to calculate a location component equal to the location of one of the samples within the signal portion, the signal portion having a boundary at the zero crossing; and

an interpolator coupled to the buffer and to the approximation circuit and operable to calculate from the location component and the samples the location of the one sample with respect to a predetermined point of the signal.

2. The circuit of claim 1 wherein:

the periodic signal comprises a sinusoid; and

the predetermined point of the signal comprises a peak of the sinusoid.

3. The circuit of claim 1 wherein the predetermined point of the signal lies at an endpoint of or outside of the portion of the signal.

4. A circuit, comprising:

a buffer operable to receive and store first raw samples of a periodic signal having a peak amplitude, the first raw samples spaced apart from each other by or approximately by half a period of the signal, the buffer operable to receive second raw samples of the signal that are spaced apart from each other by or approximately by half a period of the signal and that are respectively spaced apart from the first raw samples by or approximately by a quarter period of the signal;

a filter coupled to the buffer and operable to generate a first sample equal to an average of the first raw samples and to generate a second sample equal to an average of the second raw samples;

an approximation circuit coupled to the filter and operable to approximate a portion of the periodic signal as a straight line and to calculate a location component equal to the location of one of the first and second samples within the signal portion; and

an interpolator coupled to the filter and to the approximation circuit and operable to calculate from the location component and the first and second samples the location of the one sample with respect to a predetermined point of the signal.

5. A circuit, comprising:

a buffer operable to receive and store first and second samples of a sinusoid having a peak amplitude;

an approximation circuit coupled to the buffer and operable to approximate a half quadrant of the sinusoid as a straight line, the half quadrant having a boundary at a zero crossing of the sinusoid, the approximation circuit operable to calculate a phase angle between the zero crossing and one of the samples within the half quadrant equal to 45°

×

(the one sample)÷

[(peak amplitude)(sin 45°

)]; and

an interpolator coupled to the buffer and to the approximation circuit and operable to calculate from the phase angle and the samples the location of the one sample with respect to a predetermined point of the sinusoid.

6. A circuit, comprising:

a buffer operable to receive and store first and second samples of a sinusoid including a peak having a peak amplitude;

an approximation circuit coupled to the buffer and operable to approximate a portion of the sinusoid as a straight line and to calculate the location of one of the samples within the signal portion equal to 45°

×

(the first sample)÷

[(peak amplitude)(sin 45°

)]; and

an interpolator coupled to the buffer and to the approximation circuit and operable to calculate from the location of the one sample and the first and second samples the phase difference between the one sample and the peak of the sinusoid, the phase difference equal to,

90°

minus the location of the one sample if the first and second samples have the same polarities and the absolute value of the first sample is less than the absolute value of the second sample,

the location of the one sample if the first and second samples have the same polarities and the absolute value of the first sample is greater than or equal to the absolute value of the second sample,

180°

minus the location of the one sample if the first and second samples have opposite polarities and the absolute value of the first sample is greater than the absolute value of the second sample, and

90°

plus the location of the one sample if the first and second samples have opposite signs and the absolute value of the first sample is less than or equal to the absolute value of the second sample.

7. A method, comprising:

generating first and second samples of a periodic signal having a peak amplitude;

approximating the relative phase of one of the samples within a portion of the signal as linearly proportional to the value of the sample; and

calculating from the relative phase and the values of the samples the location of the one sample with respect to a predetermined point of the signal, the predetermined point lying at an endpoint of or outside of the portion of the signal.

8. The method of claim 7 wherein the generating comprises:

generating first raw samples that are spaced apart from each other by or approximately by half a period of the signal;

averaging the first raw samples to generate the first sample;

generating second raw samples that are spaced apart from each other by or approximately by half a period of the signal and that are respectively spaced apart from the first raw samples by or approximately by a quarter period of the signal; and

averaging the second raw samples to generate the second sample.

9. The method of claim 7 wherein:

the periodic signal comprises a sinusoid;

the portion of the signal comprises half quadrant of the sinusoid, the half quadrant having a boundary at a zero crossing of the sinusoid; and

the approximating comprises setting the relative phase equal to a phase angle of 45°

×

(the one sample)÷

[(peak amplitude)(sin 45°

)] between the one sample and the zero crossing.

10. The circuit of claim 7 wherein:

the periodic signal comprises a sinusoid; and

the predetermined point of the signal comprises a peak of the sinusoid.

11. The circuit of claim 7 wherein:

the periodic signal comprises a zero crossing; and

the portion of the signal includes a boundary at the zero crossing.

12. A read channel, comprising:

a sampler operable to sample a read signal at first and second preamble times during a preamble portion and at a first data time during a data portion, and operable to generate corresponding first and second preamble-sample values and a corresponding data-sample value;

a sample interpolator coupled to the sampler, operable to receive a phase difference between the first data time and a second data time that corresponds to a data window of the read signal, and operable to generate from the data sample value and the phase difference an adjusted sample value that equals or approximately equals the value of the read signal at the second time;

a tracking circuit coupled to the sample interpolator and operable to track and update the phase difference; and

an initial-phase circuit coupled to the sampler, sample interpolator, and tracking circuit and operable to calculate an initial value of the phase difference by,

approximating the relative phase of one of the sample times with respect to an end point of a subportion of the preamble portion of the read signal as being linearly proportional to the preamble-sample value corresponding to the one sample time, and

calculating from the relative phase and the first and second preamble-sample values the initial value of the phase difference equal to a phase difference between the one sample time and a predetermined point of the read signal, the predetermined point lying at an endpoint of or outside of the subportion of the read signal.

13. The read channel of claim 12 wherein the preamble portion of the read signal comprises a sinusoid.

14. The read channel of claim 12 wherein:

the preamble portion of the read signal comprises a sinusoid; and

the subportion of the preamble portion comprises a half quadrant of the sinusoid.

15. The read channel of claim 12 wherein:

the preamble portion of the read signal comprises a sinusoid; and

the end point of the subportion comprises a zero crossing of the sinusoid.

16. The read channel of claim 12 wherein:

the preamble portion of the read signal comprises a sinusoid; and

the predetermined point of the read signal comprises a peak of the sinusoid.

17. A read channel, comprising:

a sampler operable to sample a read signal at first and second preamble times during a preamble portion having a zero crossing and at a first data time during a data portion, and operable to generate corresponding first and second preamble-sample values and a corresponding data-sample value;

a sample interpolator coupled to the sampler, operable to receive a phase difference between the first data time and a second data time that corresponds to a data window of the read signal, and operable to generate from the data sample value and the phase difference an adjusted sample value that equals or approximately equals the value of the read signal at the second time;

a tracking circuit coupled to the sample interpolator and operable to track and update the phase difference; and

an initial-phase circuit coupled to the sampler, sample interpolator, and tracking circuit and operable to calculate an initial value of the phase difference by,

approximating the relative phase of one of the sample times within a subportion of the preamble portion of the read signal as being linearly proportional to the preamble-sample value corresponding to the one sample time, the subportion having an end point at the zero crossing of the preamble portion, and

calculating from the relative phase and the first and second preamble-sample values the initial value of the phase difference equal to a phase difference between the one sample time and a predetermined point of the read signal.

18. The read channel of claim 17 wherein the predetermined point lies at an endpoint of or outside of the subportion of the read signal.

19. The read channel of claim 17 wherein the preamble portion of the read signal comprises a sinusoid.

20. The read channel of claim 17 wherein:

the preamble portion of the read signal comprises a sinusoid; and

the subportion of the preamble portion comprises a half quadrant of the sinusoid.

21. The read channel of claim 17 wherein:

the preamble portion of the read signal comprises a sinusoid; and

the predetermined point of the read signal comprises a peak of the sinusoid.

22. A method, comprising:

generating first and second samples of a sinusoid having a peak amplitude;

approximating a relative phase of one of the samples within a portion of the sinusoid as equal to 45°

×

(the one sample)÷

[(peak amplitude)(sin 45°

)]; and

calculating from the relative phase and the values of the samples the phase difference between the one sample and a peak of the sinusoid, the phase difference being equal to,

90°

minus the relative phase if the first and second samples have the same polarities and the absolute value of the first sample is less than the absolute value of the second sample,

the relative phase if the first and second samples have the same polarities and the absolute value of the first sample is greater than or equal to the absolute value of the second sample,

180°

minus the relative phase if the first and second samples have opposite polarities and the absolute value of the first sample is greater than the absolute value of the second sample, and

90°

plus the relative phase if the first and second samples have opposite signs and the absolute value of the first sample is less than or equal to the absolute value of the second sample.

23. A disk-drive system, comprising:

a data-storage disk having a surface and operable to store a preamble and data values;

a motor coupled to and operable to rotate the disk;

a read head operable to generate a read signal that includes the preamble followed by a data portion that includes the data values, each of the data values located within a respective data window of the read signal, each of the data windows having a center;

a read-head positioning assembly operable to move the read head over the surface of the disk; and

a read channel, comprising,

a sampler operable to sample a read signal at first and second preamble times during a preamble portion and at a first data time during a data portion, and operable to generate corresponding first and second preamble-sample values and a corresponding data-sample value,

a sample interpolator coupled to the sampler, operable to receive a phase difference between the first data time and a second data time that corresponds to a data window of the read signal, and operable to generate from the data sample value and the phase difference an adjusted sample value that equals or approximately equals the value of the read signal at the second time,

a tracking circuit coupled to the sample interpolator and operable to track and update the phase difference, and

an initial-phase circuit coupled to the sampler, sample interpolator, and tracking circuit and operable to calculate an initial value of the phase difference by,

approximating the relative phase of one of the sample times with respect to an end point of a subportion of the preamble portion of the read signal as being linearly proportional to the preamble-sample value corresponding to the one sample time, and

calculating from the relative phase and the first and second preamble-sample values the initial value of the phase difference equal to a phase difference between the one sample time and a predetermined point of the read signal, the predetermined point lying at an endpoint of or outside of the subportion of the read signal.

24. A disk-drive system, comprising:

a data-storage disk having a surface and operable to store a preamble and data values;

a motor coupled to and operable to rotate the disk;

a read head operable to generate a read signal that includes the preamble followed by a data portion that includes the data values, each of the data values located within a respective data window of the read signal, each of the data windows having a center;

a read-head positioning assembly operable to move the read head over the surface of the disk; and

a read channel, comprising,

a sampler operable to sample a read signal at first and second preamble times during a preamble portion having a zero crossing and at a first data time during a data portion, and operable to generate corresponding first and second preamble-sample values and a corresponding data-sample value,

a sample interpolator coupled to the sampler, operable to receive a phase difference between the first data time and a second data time that corresponds to a data window of the read signal, and operable to generate from the data sample value and the phase difference an adjusted sample value that equals or approximately equals the value of the read signal at the second time,

a tracking circuit coupled to the sample interpolator and operable to track and update the phase difference, and

an initial-phase circuit coupled to the sampler, sample interpolator, and tracking circuit and operable to calculate an initial value of the phase difference by,

approximating the relative phase of one of the sample times within a subportion of the preamble portion of the read signal as being linearly proportional to the preamble-sample value corresponding to the one sample time, the subportion having an end point at the zero crossing of the preamble portion, and

calculating from the relative phase and the first and second preamble-sample values the initial value of the phase difference equal to a phase difference between the one sample time and a predetermined point of the read signal.