Unit for determining the sampling phase

1. An apparatus for ascertaining and correcting an optimum sampling time f or an oversampled digital bit stream in which samples are taken at n different sampling times for each bit, the apparatus comprising:

a reading unit for reading each next bit from said oversampled digital bit stream at said optimum sampling time;

a correlation determining unit for determining a correlation between a sequence of sampled data bits and a comparative sequence, said correlation determining unit providing correlation values by determining an associated correlation value at each sampling time; and

a unit for determining a new optimum sampling time from said correlation values;

said comparative sequence being a continuous bit pattern; and

said bit read at said optimum sampling time being fed into said comparative sequence.

2. The apparatus according to claim 1 , further comprising:

a comparative-sequence shift register for storing said comparative sequence;

said bit read at said optimum sampling time being fed into said comparative-sequence shift register.

3. The apparatus according to claim 1 , further comprising:

a sequence of shift registers for shifting said oversampled digital bit stream;

each one of said shift registers having n register cells for holding n samples available for each bit.

4. The apparatus according to claim 1 , wherein said optimum sampling time is determined a plurality of times during a data burst.

5. The apparatus according to claim 1 , wherein said optimum sampling time is determined a plurality of times during a data burst at cyclic intervals.

6. The apparatus according to claim 1 , wherein said comparative sequence is equated to a synchronization word at each start of reception of a data burst.

7. The apparatus according to claim 1 , wherein said optimum sampling time is varied only within a prescribed range around a previous optimum sampling time.

8. The apparatus according to claim 1 , wherein said correlation determining unit determines a hamming distance between said sequence of sampled data bits that is associated with a particular sampling time and said comparative sequence.

9. The apparatus according to claim 8 , wherein said correlation determining unit compares said hamming distance with a prescribed threshold value and if said hamming distance is below said threshold value, said correlation determining unit sets an associated correlation flag.

10. The apparatus according to claim 8 , wherein said unit for determining said new optimum sampling time determines said new optimum sampling time by considering a sampling-time range within which said hamming distance is below said prescribed threshold value.

11. The apparatus according to claim 8 , wherein:

said unit for determining said new optimum sampling time determines said new optimum sampling time by considering a sampling-time range within which said hamming distance is below said prescribed threshold value; and

said new optimum sampling time is chosen as a time that is in a center of said sampling-time range.

12. A method for ascertaining and correcting an optimum sampling time for an oversampled digital bit stream in which samples are taken at n different sampling times for each bit, the method which comprises:

reading a next bit from the oversampled digital bit stream at a previous optimum sampling time;

feeding the bit into a comparative sequence being stored as a continuous bit pattern;

determining a correlation between a sequence of sampled data bits and the comparative sequence, wherein a plurality of correlation values are obtained by determining an associated correlation value at each sampling time; and

determining a new optimum sampling time from the plurality of correlation values.

13. The method according to claim 12 , which further comprises storing the comparative sequence in a comparative-sequence shift register by feeding the bit, which has been read at the previous optimum sampling time into the comparative-sequence shift register.

14. The method according to claim 12 , which further comprises:

using a sequence of shift registers to shift the oversampled digital bit stream; and

providing each one of the shift registers with n register cells for holding n samples available for each bit.

15. The method according to claim 12 , which further comprises performing the step of determining the optimum sampling time a plurality of times during a data burst.

16. The method according to claim 12 , which further comprises performing the step of determining the optimum sampling time a plurality of times during a data burst at cyclic intervals.

17. The method according to claim 12 , which further comprises equating the comparative sequence to a synchronization word at each beginning of a reception of a data burst.

18. The method according to claim 12 , which further comprises situating the new optimum sampling time within a prescribed range around the previous optimum sampling time.

19. The method according to claim 12 , which further comprises performing the step of determining the correlation by determining a hamming distance between the sequence of sampled data bits, which is associated with a particular sampling time, and the comparative sequence.

20. The method according to claim 19 , which further comprises performing the step of determining the correlation by comparing the hamming distance, which is associated with a particular sampling time, with a prescribed threshold value, and if the hamming distance is below the threshold value, setting a correlation flag.

21. The method according to claim 19 , which further comprises performing the step of determining the new optimum sampling time by considering a sampling-time range within which the hamming distance is below a prescribed threshold value.

22. The method according to claim 21 , which further comprises choosing a time that is in a center of the sampling-time range, within which the hamming distance is below the prescribed threshold value, as the new optimum sampling time.