Browse Prior Art Database

SKEW COMPENSATION METHOD FOR MEASURING THE DIGITAL SIGNALS

IP.com Disclosure Number: IPCOM000007429D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2002-Mar-26
Document File: 5 page(s) / 282K

Publishing Venue

Motorola

Related People

Eeshat U. Ansari: AUTHOR

Abstract

Problem Caused by the Skew Effect: A digital signal is measured by collecting a number of sam- ples per level. From each level, only 'one' sample is selected as the measurement ofthat level. Other sam- ples from that level are ignored.

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@ MmROLA Technical Developments

SKEW COMPENSATION METHOD FOR MEASURING THE DIGITAL SIGNALS

by Eeshat U. Ansari

   Problem Caused by the Skew Effect: A digital signal is measured by collecting a number of sam- ples per level. From each level, only 'one' sample is selected as the measurement ofthat level. Other sam- ples from that level are ignored.

sists of exactly 365% days. It was tricky to measure this period in terms of full days. So they used the concept of leap year. In this technique, usually one year is defined to have 365 days, where as every fourth year will have 366 days (February of 29 days).

  Similarly the skew compensation method presented here calculates the difference between the two frequencies and adjusts the "measuring" unit accordingly.

  In this way, we work with the problem, rather than by changing the problem to fit one possible solution. This Skew Compensation method deserves attention because the alternative approaches are very expensive and complex to implement.

  A problem occurs, when there is even a small difference in the frequency of the incoming signal and the frequency of collecting the samples. In other words, when there is skew effect present between the two frequencies. In that situation, the sample which is supposed to measure a particular level (as described in the above paragraph) moves either to the right or to the left, from that level. This gener- ates error.

  The method below, presents a software solution, which makes it possible to measure, the incoming signal accurately, even if there is skew effect present between the two frequencies. This way, it is a lot easier to do the measurement, instead of trying to adjust one frequency to exactly match the other Frequency.

Overview of the solution: Probably it is easier to explain this method, by an example. One year con-

DESCRlPTlON OF SKEW COMPENSATlON METHOD

To describe this problem the following terms are defined:

  1. Sample: A sample is the reading or the measurement of the level as shown in the figure below. To read a level, usually more than one sam- ple are collected per level.

Selected Sample

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Level

d

Sample Sel&tor Interval

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MolylRoLA Technical Developments

  2. Sample Selector interval: To measure a level only one sample per level is selected. This sample is selected in the middle part of the level, to avoid the edges between the levels. This sample is called the Selected Sample. The distance between two con- secutive selected samples is called the sample selec- tor Interval. If this sample selector interval is meas- ured in terms of number of samples, then in dia- gram on page 35, the value will be 3. Note that the number of samples per level is also 3. So we can say, in the above diagram, that the number of samples per level is equal to the sample selector interval.

DETAILS OF THE METHOD:

by evenly dividing the level into 's' equal segmen...