Plotting Eye Diagram from ADS Data in MATLAB - matlab

Question

I have a data file (Sample_Eye_1.txt) which I obtained from the simulation plot of ADS Keysight. It has 3 fields - "Index", "Time" and "Voltage". Now the eye diagram plot will be voltage vs time. There can be different voltages at the same time at only different index. So index can be seen as a data filter field or similar like that. The plot in ADS simulation is the following
You can see that the line plot is plotted like it is superimposed on different lines.
Now when I plot data in MATLAB voltage vs time, it is not superimposed somehow. This is the plot generated plot of my matlab code which is just simple xy plot.
My MATLAB code:
% open data file
fid = fopen('Sample_Eye_1.txt');
% Read data in from csv file
readData = textscan(fid,'%f %f %f','Headerlines',1,'Delimiter',',');
% Extract data from readData
index_Data = readData{1,1}(:,1);
xData = readData{1,2}(:,1);
yData = readData{1,3}(:,1);
% Plot Data
f1 = figure(1);
cla; hold on; grid on;
%set(gca, 'XTick',[0 5 10 15 20 25 30]);
%set(gca,'XTick',0:0.1e-8:1e-8)
%set(gca,'XTickLabel',0:1:10)
plot(xData,yData,'r-');
title('Eye Diagram')
xlabel('Time(ns)')
ylabel('Density(V)')
Can anyone help me to generate the plot like the plot of ADS simulation plot?
Note: The data is big (around 2.7 Mb). If I truncate the data, the problem cannot be fully understood.

Answer 1

Your code is fine, the problem is due to the way you plot the data.
plot(xData,yData,'r-');
connects all the points with a line segment, this implies that the "holes" of the eye diagram are "closed" when the lines cross them.
You can obtain the expected plot, by simply change the "lines" with "dots"
plot(xData,yData,'r.')
If you want to have a plot more "similar" to the reference one, you can identify the input points with the same index an plot them (again, with "dots") in a loop in which, at each iteration you can change the colot of the dots.
In the following, you can find an updated versin of your code in which the loop is used to plot the data.
Edit to answer the comment
In general, you can specify the color of the marker by setting the color property either by specifying the "name" of the color or its RGB triplet (ref. to the "plot" function documentation for the details).
In your case, the "unique" indices are 16 whike the available "name" of the color are only 8 therefore you have to define the 16 color by defining explicitly the RGB triplet (which can be boring).
Notice, that the most of your data correspond to the first three indices, so, you could define three colors and let the other be random.
In the updated version of the code I've used this approach, defining the matrix dot_color as follows
dot_color=[0 0 .5
.5 .9 .9
0.9 .5 0
rand(length(uni_idx-3),3)]
this means, I've chosed the first three color and used random numbers for the others.
Of course, you can "manually define also the other colors (the value of each entry in the matrix should range between 0 and 1).
fid = fopen('Sample_Eye_1.txt');
% Read data in from csv file
readData = textscan(fid,'%f %f %f','Headerlines',1,'Delimiter',',');
fclose(fid)
% Extract data from readData
index_Data = readData{1,1}(:,1);
% Identify the unique indices
uni_idx=unique(index_Data);
xData = readData{1,2}(:,1);
yData = readData{1,3}(:,1);
% Plot Data
f1 = figure(1);
cla; hold on; grid on;
%set(gca, 'XTick',[0 5 10 15 20 25 30]);
%set(gca,'XTick',0:0.1e-8:1e-8)
%set(gca,'XTickLabel',0:1:10)
% plot(xData,yData,'r-');
% Loop over the indices to plot the corresponding data
% Define the color of the dots
dot_color=[0 0 .5
.5 .9 .9
0.9 .5 0
rand(length(uni_idx-3),3)]
for i=1:length(uni_idx)
idx=find(index_Data == uni_idx(i));
% plot(readData{1,2}(idx,1),readData{1,3}(idx,1),'.')
plot(readData{1,2}(idx,1),readData{1,3}(idx,1),'.','color',dot_color(i,:))
end
title('Eye Diagram')
xlabel('Time(ns)')
ylabel('Density(V)')