Author Topic: Yet another fast edge pulse generator  (Read 78832 times)

0 Members and 1 Guest are viewing this topic.

Online 2N3055

  • Super Contributor
  • ***
  • Posts: 2024
  • Country: hr
Re: Yet another fast edge pulse generator
« Reply #525 on: May 23, 2019, 04:32:00 pm »
For a 3.5 GHz scope with BNC/SMA  converter about 150 something psec sounds fine to me ..
It is 20GHz bandwidth scope but on ProLink inputs. He used ProBus input, that one has 3.5 GHz bandwidth...
No, as far as I understood his message, in the last 2 screenshots he used the HF-input ProLink with the appropriate adapter.
If it is not, let him correct.


Sorry I wasn't paying attention.. I looked at first two ones .. |O
Thanks for pointing it out.
On two second ones he has quite a spread between minimum and maximum values, probably something wrong with connection.

 

Offline MegaVolt

  • Regular Contributor
  • *
  • Posts: 127
  • Country: by
Re: Yet another fast edge pulse generator
« Reply #526 on: May 24, 2019, 09:30:14 am »
Your screen captures show about 1.2V signal amplitude. 
Try reducing it to 700-900mV.  Higher amplitude increases edge rise time on this particular pulser.
Leo

So much better.

 

Offline Converter

  • Regular Contributor
  • *
  • Posts: 159
  • Country: ua
Re: Yet another fast edge pulse generator
« Reply #527 on: May 24, 2019, 01:43:33 pm »
So much better.
You incorrectly set the cursors. You must count (10/90%) from the level of the flat plateau on the signal. For this you need to increase the time of the review. Usually, LeCroy automatic measurements do this correctly.
Also, you need to turn on the equivalent sampling mode (if you are not going to demonstrate the Nyquist Theorem here?).
« Last Edit: May 24, 2019, 01:48:35 pm by Converter »
 

Offline MegaVolt

  • Regular Contributor
  • *
  • Posts: 127
  • Country: by
Re: Yet another fast edge pulse generator
« Reply #528 on: May 24, 2019, 02:24:57 pm »
You incorrectly set the cursors. You must count (10/90%) from the level of the flat plateau on the signal. For this you need to increase the time of the review.
I set the thresholds exactly as you described. And then stretched the signal.
Quote
Usually, LeCroy automatic measurements do this correctly.
OK. No problems. Look at the bottom left for the numbers that Lecroy counted automatically.
Quote
Also, you need to turn on the equivalent sampling mode (if you are not going to demonstrate the Nyquist Theorem here?).
I do not understand. 80 gigasamples per second is not enough? This is a two-fold reserve from the Nyquist frequency.
 

Offline rhb

  • Super Contributor
  • ***
  • Posts: 2616
  • Country: us
Re: Yet another fast edge pulse generator
« Reply #529 on: May 24, 2019, 06:55:17 pm »
FWIW My LeCroy DDA-125/LC684DLX samples at 2 GSa/s with a 1.5 GHz anti-alias filter.

You can get away with being slightly undersampled as long as you do not go into the frequency domain.

I just received a pair of custom pulsers which produce a 1 MHz square wave instead of the standard 10 MHz.  I wanted these to allow using a cheap DSO for TDR work.

I'll test them and compare the BNC to SMA connection against the 20 ps calibrator output of my Tek 11801.
 

Offline Converter

  • Regular Contributor
  • *
  • Posts: 159
  • Country: ua
Re: Yet another fast edge pulse generator
« Reply #530 on: May 24, 2019, 08:50:32 pm »
I do not understand. 80 gigasamples per second is not enough? This is a two-fold reserve from the Nyquist frequency.
You incorrectly apply the Nyquist Theorem. It depends on what you want to do. In this case, you have only 4-5 sample points on the rising edge, but at least 10 is recommended for reliable measurements: https://blog.teledynelecroy.com/2016/09/how-does-sampling-rate-affect-esd-pulse.html

Quote
I set the thresholds exactly as you described. And then stretched the signal.
Quote
OK. No problems. Look at the bottom left for the numbers that Lecroy counted automatically.
You should not have reduced the acquisition area to such an extent, since automatic measurements are made in the range of the captured image.
« Last Edit: May 24, 2019, 08:57:19 pm by Converter »
 

Offline Berni

  • Super Contributor
  • ***
  • Posts: 2332
  • Country: si
Re: Yet another fast edge pulse generator
« Reply #531 on: May 25, 2019, 11:25:08 am »
Yeah you need enough definition in the edge to reliably find the 90% and 10% marks. Often the waveform is particularly curvy there so just linear interpolation could be off quite a bit.

Theoreticaly you could use sin(x)/x interpolation to reconstruct the area between the points as long as you meet the f/2 Nyquist requirement to get a perfect representation of the waveform between the points,  thus letting you pick that magical 90% point reliably. However this only works if there is a brick wall filter at f/2. Oscilloscopes however have all sorts of different high frequency rolloff responses in there AFE (There are pros and cons to different ones too). Because of this the usual sin(x)/x interpolation won't be completely accurate (but still likely quite a bit closer to the real thing than linear interpolation). Dave recently did a good video related to this on scope interpolation.

So this is why its nice to have more points. For repeating waveforms such as this pulse generator its easy to get around the ADC sampling rate limitation by just turning on equivalent time sampling. This captures multiple edges and uses extra phase information from the trigger circuitry to determine the exact transition so that the scope can then merge the points together into single waveform with 100s of times more points, getting you a nice non-jaggy image of that edge. You do get some extra fuzziness because the trigger circuitry has some inherent amplitude and phase noise, the ADC clock has some amount of phase noise and the input signal has some noise in itself, but this can be easily taken care of using some averaging.
 

Offline MegaVolt

  • Regular Contributor
  • *
  • Posts: 127
  • Country: by
Re: Yet another fast edge pulse generator
« Reply #532 on: May 26, 2019, 12:06:45 pm »
You incorrectly apply the Nyquist Theorem. It depends on what you want to do. In this case, you have only 4-5 sample points on the rising edge, but at least 10 is recommended for reliable measurements: https://blog.teledynelecroy.com/2016/09/how-does-sampling-rate-affect-esd-pulse.html
I quite well understand the Nyquist theorem. And by itself, if we want to see the shape of the pulse front, we should have a tenfold frequency margin at a minimum. Those. if we want to consider a square wave of 1Hz, we need an oscilloscope with a sampling frequency > 20 Hz.

However, if we want to EVALUATE the bandwidth of the oscilloscope, then we do not need such a large stock. Again, the input from the pulser has a lower frequency than the input frequency of the oscilloscope. Approximately 0.35 / 0.034 = 10 GHz. This means 8 points per maximum signal frequency.

But if you are interested in looking at the details of the front, i can turn on the desired mode.

Quote
I set the thresholds exactly as you described. And then stretched the signal.
You should not have reduced the acquisition area to such an extent, since automatic measurements are made in the range of the captured image.[/quote]Yes, maybe I did not take into account this nuance in his work. I will retake the data.

For repeating waveforms such as this pulse generator its easy to get around the ADC sampling rate limitation by just turning on equivalent time sampling.
Yes, without a doubt. I did just quick measurements about the same as all the others in the subject. And I don’t really understand what caused such a great interest in my pictures? What would you like to see? I am sure that any further refinements will not greatly change the picture on the screen.

So what exactly do you expect to see in the picture?
 

Offline MegaVolt

  • Regular Contributor
  • *
  • Posts: 127
  • Country: by
Re: Yet another fast edge pulse generator
« Reply #533 on: May 27, 2019, 11:08:48 am »
New pictures.
 

Offline capt bullshot

  • Super Contributor
  • ***
  • Posts: 1582
  • Country: de
    • Mostly useless stuff, but nice to have: wunderkis.de
Re: Yet another fast edge pulse generator
« Reply #534 on: July 17, 2019, 11:25:56 am »
This is the "world's fastest" Hantek DSO5062B (hacked and modified by forum user tatus1969):




in comparison to a plain vanilla Tek TPS2024

Safety devices hinder evolution
 

Offline magic

  • Frequent Contributor
  • **
  • Posts: 855
  • Country: pl
Re: Yet another fast edge pulse generator
« Reply #535 on: July 17, 2019, 04:35:25 pm »
I could swear my unmodified Hantek 5102B managed 1.7ns with just a software unlock and tatus1969 claimed that he got his down to 1.5ns.
 

Offline capt bullshot

  • Super Contributor
  • ***
  • Posts: 1582
  • Country: de
    • Mostly useless stuff, but nice to have: wunderkis.de
Re: Yet another fast edge pulse generator
« Reply #536 on: July 17, 2019, 08:18:45 pm »
I could swear my unmodified Hantek 5102B managed 1.7ns with just a software unlock and tatus1969 claimed that he got his down to 1.5ns.
Confirmed, he made some "special" terminators, using one of these, I can achieve 1.5ns. The above measurement was taken with a standard 50 Ohm inline terminator attached between the pulse generator and the scope.
Safety devices hinder evolution
 

Offline TiN

  • Super Contributor
  • ***
  • Posts: 4029
  • Country: tw
  • xDevs.com/live - 24/7 lab feed
    • xDevs.com
Re: Yet another fast edge pulse generator
« Reply #537 on: August 30, 2019, 10:12:02 am »
 :-+ Bought one of these pulse generators from Leo, thanks! Splurged for fastest 2.92mm version (and had to buy $70 adapter separately, I'd wish there would a version in shop to include proper 2.92mm adapter, instead of cheap SMA).







Here are some quick and dirty results:

Tek DSA71604C





Tek TDS7704B



Tek DPO7254C



Tek MDO4054C





YouTube | Chat room | Live-cam | Have documentation to share? Upload here! No size limit, firmware dumps, photos.
 
The following users thanked this post: edavid

Offline rhb

  • Super Contributor
  • ***
  • Posts: 2616
  • Country: us
Re: Yet another fast edge pulse generator
« Reply #538 on: August 31, 2019, 03:12:40 am »
My 11801 calibrator and my SD-24 head will beat Leo's pulser, but only by a few ps. 

I think Leo's pulsers are fantastic.  I've got the standard 10 MHz plus a 100 ps impulse and a 1 MHz square wave custom all in BNC.  I'll add an impulse in 3.5 mm  if Leo will oblige and can beat the 100 ps BNC version.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf