5444B AWG jitter

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germanium
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Joined: Wed May 23, 2018 10:53 am

5444B AWG jitter

Post by germanium »

I'am new on this forum and using the pico scope for some time.
Now I am testing the AWG function and have a question about it's performance

Application
Important for the setup, is a low amount of jitter.
In order to reduce the jitter, I use two output pulses of the AWG, with 56us separation.
The first pulse is the stimulus of the system to test, the 2nd pulse is used as a sync pulse for the scope

Conclusion
Found jitter on the AWG output is 5ns.
What is wrong with my setup?

Details
Scope setup
- 500Ms/s, 8bit
- Channel A,
- Trigger on channel A
- 20MHz lowpass filter enabled

AWG setup
- Start frequency : 10kHz
- 20000 (20k) samples
- waveform: does have 2pulses, see "Generated waveform":
1st pulse = stimulus = 1 period 4MHz square wave at 10us amplitude = 0.9
2nd pulse = sync pulse = 0.5period 4MHz square wave, amplitude = 0.5
delay with stimulus is : 1us, 9us and 59us

Found jitter
1. at stimulus : barely visible, only some scope jitter
2. at sync pulse -1us delay - : no jitter visible
3. at sync pulse -9us delay- : 5ns jitter
4. at sync pulse -59us delay- : 5ns jitter

Gerry
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Re: 5444B AWG jitter

Post by Gerry »

Hi germanium,

So, do I understand you correctly, is what you are saying that you have 2 pulses per capture, one that you are triggering on (to, as you say synchronize the signal Generator output with the PicoScope sample clock), and the other one to measure the jitter?

Could you post the Psdata file for what you are describing.

Regards,

Gerry
Gerry
Technical Specialist

germanium
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Joined: Wed May 23, 2018 10:53 am

Re: 5444B AWG jitter

Post by germanium »

Hi Gerry,

Thanks for replying me.

I will replay the effects I described, since I did not save psdata - size is about 20MByte! -.
At least I do have some pictures / screendumps of it (but I don't know how to post them)

Currently I am doing some more tests at 125Ms/s /+ rapid trigger / 12bit in combination with the AWG.

Gerry
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Re: 5444B AWG jitter

Post by Gerry »

Hi Germanium,

Actually there's no need to post a psdata file now that I know what you are doing.

Looking at the specifications for the B model 5000 series PicoScopes (https://www.picotech.com/oscilloscope/5 ... ifications) the update rate is 200MS/s, so the update interval is 5ns, which means that there will be an uncertainty of 5ns on the edge of a square wave, which is what you found.

Regards,

Gerry
Gerry
Technical Specialist

germanium
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Joined: Wed May 23, 2018 10:53 am

Re: 5444B AWG jitter

Post by germanium »

Hi Gerry

I doubt we are talking about the same thing.
This is how I understand it:
1. In a CSV file, I define a stimulus of two pulses, each 4MHz, distance between the 2 pulses varies between 2 and 50us. This time-distance is constant during one set of measurements.
2. This file is read by picoscope,each sample has a fixed position (for instance sample 10000 = 1V).
3. The AWG signal is repeated every 1ms, scope triggers on it (CH3, rapid trigger).
4. Data is sampled and stored, 10.000 waveforms
5. in Matlab / Excel data is analyzed.

Now , depending on the time between the first and second pulse, a number of waveforms deviate 5ns.
The larger the time, the more waveforms deviate.

See the attached pdf file.
(A number of plot's removed to reduce it's size)
Attachments
AWG picoscope.pdf
(411.23 KiB) Downloaded 325 times

Gerry
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Re: 5444B AWG jitter

Post by Gerry »

Hi geranium,

The reason for the variation that you see was given at the bottom of this post by Martyn: post44027.html?hilit=5ns#p44027.

So, if your waveform edges are not exactly on a 5ns boundary, relative to the trigger point, then you will see a variation for the edges that will increase in occurrences the closer the edge is to a midpoint between two 5ns boundaries (e.g. at 7.5ns). As an example I have 3 psdata files that have 500 captures, and you can scroll through a few to see the effect on the leading edge of the second pulse by clicking on the compass icon. Here are the files:
Updaterate variation examples.zip
(11.44 MiB) Downloaded 307 times

The data file for the pulse spacing of approx 49us shows 26 variations in the last 100 waveforms, The file for the pulse spacing of approx 5us spacing shows only 12 variations in the last 100, but the file for the spacing of exactly 5us shows no variations at all.

So, for the 5000 series PicoScopes, if you want to avoid variations of 5ns in the positioning of further pulse edges relative to the trigger point, you need to use spacings that are exact multiples of 5ns.

Regards,

Gerry
Gerry
Technical Specialist

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