Method and apparatus for jitter analysis

Abstract

A method, apparatus, and article of manufacture for separating the components of a jitter signal. The method includes the steps of obtaining measurements of the spans of a signal, generating variation measurements for each of the spans, transforming the variation estimates from a time domain to a frequency domain, and determining the random component and the periodic component of the jitter signal.

What is claimed is:  
     
         1 . A method of analyzing jitter in a signal having transitions which define spans over a time interval, the jitter having a random component and a periodic component, comprising the steps of: 
 (a) obtaining a plurality of measurements for a plurality of spans;    (b) generating variation estimates for the measurements for each of the spans;    (c) transforming the variation estimates from a time domain to a frequency domain; and    (d) determining the random component and the periodic component of the jitter signal.    
     
     
         2 . The method of  claim 1 , wherein the determining step comprises the step of applying a constant false alarm filter to the frequency domain variation estimates to separate the random component and the periodic component.  
     
     
         3 . The method of  claim 2 , wherein the transforming step is performed through a FFT.  
     
     
         4 . The method of  claim 1 , wherein the variation estimates comprise variance estimates.  
     
     
         5 . A method of analyzing jitter in a signal having a repetitive data pattern comprising transitions which define spans over a time interval, the jitter having a random component and a periodic component, comprising steps of: 
 (a) measuring a unit interval of the data pattern;    (b) determining a matching pattern;    (c) calculating a measurement schedule defining a measurement set for each span;    (d) obtaining a plurality of measurements for a plurality of spans;    (e) generating variation estimates for the measurements for each of the spans;    (f) transforming the variation estimates from a time domain to a frequency domain; and    (g) determining the random component and the periodic component of the signal.    
     
     
         6 . The method of  claim 5 , wherein the jitter comprises an ISI component and a DCD component, the determining a matching pattern step comprising the step of calculating ISI and DCD based on a comparison of the matching pattern and the measurements.  
     
     
         7 . The method of  claim 5 , wherein the determining a matching pattern step further comprises the steps of: 
 rotating a reference pattern through a plurality of rotations;    comparing the rotations to the data pattern; and    choosing the matching pattern.    
     
     
         8 . The method of  claim 7 , wherein the comparing step comprises the step of comparing the rotations to the data pattern by the least-squared method.  
     
     
         9 . The method of  claim 5 , wherein the determining the random component and the periodic component step comprises the step of applying a constant false alarm filter to the frequency domain variation estimates to separate the random component and the periodic component.  
     
     
         10 . The method of  claim 5 , wherein the transforming step is performed through a FFT.  
     
     
         11 . The method of  claim 5 , wherein the variation estimates comprise variance estimates.  
     
     
         12 . The method of  claim 5 , further comprising the step of measuring the statistical confidence of the unit interval.  
     
     
         13 . The method of  claim 2 , further comprising the step of measuring the statistical confidence of the matching pattern.  
     
     
         14 . An apparatus for analyzing jitter in a signal having a repetitive data pattern comprising transitions which define spans over a time interval, the jitter having a random component and a periodic component, the apparatus comprising: 
 (a) a measurement apparatus for collecting data;    (b) an analyzing unit, operatively connected to the measurement apparatus, for collecting data from the measurement apparatus, for measuring a unit interval of the data pattern, for determining a matching pattern, for calculating a measurement schedule defining a measurement set for each span, for obtaining a plurality of measurements for a plurality of spans, for generating variation estimates for the measurements for each of the spans, for transforming the variation estimates from a time domain to a frequency domain; and for determining the random component and the periodic component of the signal.    
     
     
         15 . The apparatus of  claim 14 , wherein the analyzing unit further comprises: 
 means for calculating ISI and DCD based on a comparison of the matching pattern and the measurements.    
     
     
         16 . The apparatus of  claim 14 , wherein the analyzing unit further comprises: 
 means for applying a constant false alarm filter to the frequency domain variation estimates.    
     
     
         17 . An article of manufacture comprising a program storage medium readable by a computer having a memory, the medium tangibly embodying one or more programs of instructions executable by the computer to perform method steps for analyzing jitter in a signal having a repetitive data pattern comprising transitions which define spans over a time interval, the jitter having a random component and a periodic component, the method comprising the steps of: 
 (a) measuring a unit interval of the data pattern;    (b) determining a matching pattern;    (c) calculating a measurement schedule defining a measurement set for each span;    (d) obtaining a plurality of measurements for a plurality of spans;    (e) generating variation estimates for the measurements for each of the spans;    (f) transforming the variation estimates from a time domain to a frequency domain; and    (g) determining the random component and the periodic component of the signal.