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Show us your square wave

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tautech:

--- Quote from: Teneyes on January 28, 2015, 01:07:12 am ---
--- Quote from: tautech on January 28, 2015, 12:51:46 am ---Source?

--- End quote ---
NO source!,
I was leading you on,
I saved a waveform data ,
I then Patched the Data. to values to show a step change.
I then loaded it back into the DSO.  ;D

I thought everyone could see it was too prefect.

--- End quote ---
I figured as much  ;) and know now to watch out for any waveforms you might post.  :-DD

Electro Fan:
How should these colors be interpreted - what do they signify or represent?  Thanks

Jay_Diddy_B:
Hi,

I had a look at this picture:



I can explain it. The square wave is 15 MHz, so the spectral lines in the FFT should be 15MHz apart. From the shape of the waveform I would expect to see the higher order harmonics attenuated.

The FFT shows spectral lines that are 5 GHz apart. This is sampling frequency of the scope 5G samples per second. The Lecroy scope is using RIS acquisition.

Regards,

Jay_Diddy_B

Wuerstchenhund:

--- Quote from: Electro Fan on January 28, 2015, 07:38:30 am ---How should these colors be interpreted - what do they signify or represent?  Thanks

--- End quote ---

The picture is a 3D color persistence screen, which is essentially a more advanced variant of the common 2D persistence function many scopes have today.

Most scopes have a monochrome persistence function (i.e. intensity grading) where individual waveforms overlap each other on a single "depth" layer (the screen plane) and where the brightness represents the amount of times a waveform has passed through a particular spot on the screen. This can be used (in limits) to see jitter or other signal anomalies. More advanced scopes use color grading, i.e. the color shows how often a waveform has passed through a particular spot, where red ('hot') shows places of high occurrence, yellow for medium occurrence and blue for low occurrence.

In a 3D persistence screen each waveform is 'stacked' on top of the other, which shows much better how the waveforms change over time. Again, the colors indicate the occurrence of a waveform passing through a certain spot in the horizontal (x/y) plane.

It's a great tool but for this specific exercise I don't think it adds any value, and since the scope was running in RIS (ETS) mode I'm not sure the waveform that is displayed has much to do with the input signal. The picture shows noticeable variations in the waveform, which means RIS is unsuitable here.

T3sl4co1l:
Or to put it another way, it's a histogram of the waveform hitting those x,y (time/voltage, frequency/amplitude) points.  If you set up an external clock trigger and play random data, you automatically get your eye diagram that way.

Tim

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