Code covered by the BSD License

# Agilent Infiniium and InfiniiVision Oscilloscopes – MATLAB Example

### Vinod Cherian (view profile)

17 Dec 2008 (Updated )

MATLAB application example for Agilent Infiniium and InfiniiVision oscilloscopes

jitter(Data,Time)
```function varargout = jitter(Data,Time)
% JITTER Calculate difference between data clock and measured clock
% transitions
%
%  Usage:
%  [X,Y]   = JITTER(DATA,TIME);
%
%    MATLAB Code that is executed:
%
%    sig   = (Data>guardband) - (Data<-guardband);
%    idx   = find(sig);
%    w     = find(diff(sig(idx)));
%    idx1  = idx(w);
%    idx2  = idx(w+1);
%    y1    = waveform(idx1);
%    y2    = waveform(idx2);
%    fData = ((idx1 - y1.*(idx2-idx1)./(y2-y1))-1)/Fs;

% \$Author: Jliu \$
% \$Revision: 3 \$
% \$Date: 3/04/05 4:24p \$

% Local Functions Defined:
%

% \$Notes:
%
% \$EndNotes

% \$Description:
%
% \$EndDescription

%   Copyright 1996-2012 The MathWorks, Inc.

if nargout ==3
varargout{1} = 'Time [sec]';
varargout{2} = 'Jitter [sec]';
varargout{3} = 'Calculate difference between data clock and measured clock transitions';
return;
end;

if nargin==0
help(mfilename)
return;
end;

%Remove mean
Data=Data-mean(Data);

% I use a guardband in case of noise.
guardband = max(Data)*0.01;

sig = (Data>guardband) - (Data<-guardband);

% Find the index of all the points outside of the guardband
idx  = find(sig);

% Generate indexes of when we transition from one state to the other.
%   Remember a derivative (diff) is zero for constant values and a number if there is a change.
w = find(diff(sig(idx)));
idx1 = idx(w);              % Valid Point before Crossing state
idx2 = idx(w+1);            % Valid Point after Crossing

y1 = Data(idx1); y2 = Data(idx2); % Get y values for interp
Fs=1/(Time(2)-Time(1));
% Find Crossing using linear interpolation.
%   index_value = current_index - current_y/slope
%   Times are the index_value/SampleRate.
edgetimes = ((idx1 - y1.*(idx2-idx1)./(y2-y1))-1)/Fs;
edgetimes=edgetimes;

% derive the clocks based on the supplied symbol rate
if length(edgetimes)<2
varargout{1:2} = [];
return;
else
symbolRate = 1/min(diff(edgetimes));
clocks=round(edgetimes*symbolRate);
end;

% fit the derived clocks and the measured time to a straight line
if length(clocks)>2
coef = polyfit(clocks, edgetimes, 1);
% y = a + bx
slope = coef(1);
intercept = coef(2);

% Reconstruct the time from Fitted values.
reconstructedTime = intercept + (clocks * slope);

% Jitter is the difference between the measured time and the reconstructed time.
jitterData = reconstructedTime - edgetimes;

varargout{1} = reconstructedTime;
varargout{2} = jitterData;
else
varargout{1:2} = [];
return;
end;

```