Adaptive filtering method and apparatus to compensate for a frequency difference between two clock sources

• US 6,038,254 A
• Filed: 06/10/1998
• Issued: 03/14/2000
• Est. Priority Date: 06/07/1996
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Hoke, Joseph Michael, Patel, Samir Kirit, Ferraiolo, Frank David
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): WEBSTER, BRYAN E
• Application Number:
  US09/090,026
• Time in Patent Office: 643 Days
• Field of Search: 375/316, 375/326, 375/327, 375/344, 375/232, 375/354, 375/362, 327/23, 327/24, 327/39, 327/40, 455/182.2, 455/182.1
• US Class Current: 375/232
• CPC Class Codes: H03M 9/00 Parallel/series conversion or vice versa digital stores in which the information is moved stepwise per se G11C19/00
• CPC Class Codes: H04L 7/0331 with a digital phase-locked loop [PLL] processing binary samples, e.g. add/subtract logic for correction of receiver clock H04L7/0337 takes precedence

Abstract

Frequency differences between differing clock sources are compensated for by an adaptive filtering mechanism. An amount of frequency drift between two clock sources is determined. Then, based on that amount of frequency drift, a filtering value is selected to be used in tracking the frequency drift. If the frequency drift is determined to be large, then a minimum filtering value is selected. However, if it is determined to be small, then a maximum filtering value is selected. The selected filtering value is used to adjust the address(es) of one or more data bits being transmitted and received using the two clock sources, such that the frequency drift is properly tracked.

Claims

1. An adaptive filtering method usable in the transmission and receipt of data, said method comprising:

determining an amount of frequency drift between a first clock used in transmitting data and a second clock used in receiving said data, wherein said data comprises a plurality of data bits;

selecting, responsive to said determining, a filtering value to be used in tracking said frequency drift; and

tracking said frequency drift using a plurality of edge detectors, each of said plurality of edge detectors determining an edge of one of said plurality of data bits.

2. The method of claim 1, wherein said determining of said edge comprises providing, by said edge detector, an adjustment to an address of said edge, said providing employing said filtering value to determine when to adjust said address.

3. The method of claim 2, wherein said providing comprises providing said filtering value to a random walk filter prior to said adjustment, wherein said random walk filter determines when to adjust said address.

13. the method of claim 1, wherein said second clock is not transmitted with or extracted from said data.

4. An adaptive filtering method usable in the transmission and receipt of data, said method comprising:

determining an amount of frequency drift between a first clock used in transmitting data and a second clock used in receiving said data; and

selecting, responsive to said determining, a filtering value to be used in tracking said frequency drift, wherein said selecting comprises selecting a minimum filtering value when said frequency drift is determined to be large and a maximum filtering value when said frequency drift is determined to be small.

5. An adaptive filtering method usable in the transmission and receipt of data, said method comprising:

determining an amount of frequency drift between a first clock used in transmitting data and a second clock used in receiving said data, wherein said data comprises a plurality of data bits;

selecting, responsive to said determining, a filtering value to be used in tracking said frequency drift; and

adjusting an address of one or more data bits of said plurality of data bits to track said frequency drift, said adjusting comprising using said filtering value to determine when to adjust said address of said one or more data bits.

6. An adaptive filtering apparatus comprising:

means for determining an amount of frequency drift between a first clock used in transmitting data and a second clock used in receiving said data, wherein said data comprises a Plurality of data bits;

a selector coupled to said means for determining, said selector adapted to select, responsive to said determining, a filtering value to be used in tracking said frequency drift; and

a plurality of edge detectors adapted to track said frequency drift, each of said plurality of edge detectors being adapted to determine an edge of one of said plurality of data bits.

7. The apparatus of claim 6, wherein each of said plurality of edge detectors is further adapted to provide an adjustment to an address of said edge of said one of said plurality of data bits, wherein said filtering value is employed to determine when to adjust said address.

8. The apparatus of claim 7, further comprising a random walk filter programmable to receive said filtering value prior to said adjustment, wherein said random walk filter is further programmable to determine when to adjust said address.

9. An adaptive filtering apparatus comprising:

means for determining an amount of frequency drift between a first clock used in transmitting data and a second clock used in receiving said data; and

a selector coupled to said means for determining, said selector adapted to select, responsive to said determining, a filtering value to be used in tracking said frequency drift, wherein said selector comprises means for selecting a minimum filtering value when said frequency drift is determined to be large and a maximum filtering value when said frequency drift is determined to be small.

10. An adaptive filtering apparatus comprising:

means for determining an amount of frequency drift between a first clock used in transmitting data and a second clock used in receiving said data, wherein said data comprises a plurality of data bits;

a selector coupled to said means for determining, said selector adapted to select, responsive to said determining, a filtering value to be used in tracking said frequency drift; and

means for adjusting an address of one or more data bits of said plurality of data bits to track said frequency drift, said means for adjusting comprising said filtering value to be used in determining when to adjust said address of said one or more data bits.

11. An adaptive filtering apparatus comprising:

a monitor adapted to determine an amount of frequency drift between a first clock used in transmitting data and a second clock used in receiving said data, wherein said data comprises a plurality of data bits;

a selector adapted to select, responsive to the determining, a filtering value to be used in tracking said frequency drift; and

a plurality of edge detectors adapted to track said frequency drift, each of said plurality of edge detectors being adapted to determine an edge of one of said plurality of data bits.

12. The apparatus of claim 11, wherein said monitor and said selector are included in one unit.