Author Topic: Yet another fast edge pulse generator  (Read 147334 times)

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Offline texaspyro

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Re: Yet another fast edge pulse generator
« Reply #350 on: February 21, 2018, 12:28:21 am »
Earlier I posted a plot of the pulser output frequency and ADEVs.  The freq is with a couple of Hz... good enough to calibrate most scopes considering they usually have crappy time base oscillators.
 

Offline Insatman

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Re: Yet another fast edge pulse generator
« Reply #351 on: February 21, 2018, 01:08:00 am »
Here are some waveforms from a Tek784D.   The overshoot on the longer timescale trace isn't real but a result of the slow sampling at that sweep speed.   Note how flat the pulse is.  Nice for step testing.
The 784 is rated at 1 Ghz giving an implied risetime of 350ps....easily met.    Thanks Leo for a great product.   I've built many "fast" pulsers in my time, most much slower than his but at higher output voltage.  This unit is really nice for testing my scopes.
« Last Edit: February 21, 2018, 01:09:58 am by Insatman »
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Offline Gixy

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Re: Yet another fast edge pulse generator
« Reply #352 on: February 21, 2018, 06:29:41 am »
1GHz is 35 ps, not 350 ps  :D
 

Offline KE5FX

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Re: Yet another fast edge pulse generator
« Reply #353 on: February 21, 2018, 06:49:18 am »
1GHz is 35 ps, not 350 ps  :D

Must be those newfangled metric picoseconds. :)
 

Offline Insatman

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Re: Yet another fast edge pulse generator
« Reply #354 on: February 21, 2018, 09:08:54 am »
1GHz is 35 ps, not 350 ps  :D

lol...I wish...Formula is 1/f x .35 or 1Ghz = 350ps.  Look it up at Tektronix.
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Offline texaspyro

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Re: Yet another fast edge pulse generator
« Reply #355 on: February 21, 2018, 03:52:35 pm »
Must be those newfangled metric picoseconds. :)

Nope,  Chineseium picoseconds.
 

Offline Cerebus

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Re: Yet another fast edge pulse generator
« Reply #356 on: February 21, 2018, 04:38:58 pm »
1GHz is 35 ps, not 350 ps  :D

Must be those newfangled metric picoseconds. :)

That's 4 61/508" divided by the speed of light*, for you colonial types.  :)

* 14,238,992,130,000 inches per milli-fortnight.
« Last Edit: February 21, 2018, 04:44:44 pm by Cerebus »
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Offline texaspyro

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Re: Yet another fast edge pulse generator
« Reply #357 on: February 21, 2018, 08:24:51 pm »
* 14,238,992,130,000 inches per milli-fortnight.

I once worked for a company that required each project to have a zillion different pieces of documentation that nobody ever read.  I wrote one spec where all the timings were in units of ffn... femto-fortnights.   It was three years before anybody noticed and asked what a ffn was.
 
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Offline Gixy

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Re: Yet another fast edge pulse generator
« Reply #358 on: February 22, 2018, 06:31:13 am »
Oops, not well awaken yesterday morning, sorry  |O
 

Offline Insatman

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Re: Yet another fast edge pulse generator
« Reply #359 on: February 22, 2018, 08:46:08 am »
Oops, not well awaken yesterday morning, sorry  |O

It's ok...we all have those moments....more often as we get older it seems...
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Online Berni

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Re: Yet another fast edge pulse generator
« Reply #360 on: February 22, 2018, 01:10:00 pm »
* 14,238,992,130,000 inches per milli-fortnight.

I once worked for a company that required each project to have a zillion different pieces of documentation that nobody ever read.  I wrote one spec where all the timings were in units of ffn... femto-fortnights.   It was three years before anybody noticed and asked what a ffn was.

Hah nice one.

But did you specify weather you used the imperial or metric fortnight? Oh and does it also take in account leap seconds or the earth slowing down overtime?
 

Offline rhb

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Re: Yet another fast edge pulse generator
« Reply #361 on: February 28, 2018, 11:19:39 pm »
I'm a little nervous about damage either mechanical or ESD.  I had thought to put a small metal plate on the back, but the screws appear to be staked down. 

I'm contemplating a U shaped piece of aluminum with a U cutout for the BNC  and then securing it with epoxy on both sides. However, I don't see a good way to ground it.  I don't know if grounding it is good or bad. 

Leo?  Anyone else?

Edit:  I got a piece of heatshrink big enough to get the pulser in.  I cut Xs for the connectors (2nd try) and it went well.  Photos attached.
« Last Edit: March 05, 2018, 12:33:43 am by rhb »
 

Offline Ghislain

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Re: Yet another fast edge pulse generator
« Reply #362 on: March 21, 2018, 04:53:26 pm »
Reading through this thread makes me envious of some of the scopes shown here  :-+
Here are the results for the RTB2004 (100 MHz) with a 50 ohm pass through terminator.
According to the R&S specsheet the 100MHz model should have a rise time of <3.5ns
Measured average rise time for the 100 MHz model is 1.85ns which calculates to a bandwidth of 189 MHz.
« Last Edit: March 21, 2018, 07:23:23 pm by Ghislain »
 

Offline SWR

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Re: Yet another fast edge pulse generator
« Reply #363 on: March 22, 2018, 06:02:03 am »
I got my LB generator last night am I'm very satisfied with it. :-+
To protect the SMD componets I printed a small housing for it and uploaded the STL file here:
https://www.eevblog.com/forum/testgear/gw-instek-mdo-2000e/msg1458487/#msg1458487

My GW Instek MDO-2204EX has 1,22ns rise and fall time. Plenty fast for the work I do. :-/O
You should never go down on equipment!
 
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Offline SWR

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Re: Yet another fast edge pulse generator
« Reply #364 on: March 23, 2018, 03:06:45 pm »
I measured a Keysight DSOX3014T we have at work today.
It is 2,90ns comparable to 120MHz analog bandwidth.
The specification is 100MHz.
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Offline rhb

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Re: Yet another fast edge pulse generator
« Reply #365 on: May 22, 2018, 07:05:12 pm »
I just measured my  newly arrived MSOX3104T purchased from Keysight  "slightly used" via the webstore.  This came with fresh cal, all accessories and a 3 year warranty.  It was *not* cheap.

Measured rise time is 436 pS  which works out to 802.7 MHz  :-( 

I went to the datasheet and checked.  The spec is 1 GHz and rise time of <450 pS.  The 500 MHz version has a 700 pS risetime listed.   I'm deeply disappointed in Keysight fudging a specification like that.  It doesn't really matter for what I expect to do.
 

Offline GerryBags

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Re: Yet another fast edge pulse generator
« Reply #366 on: May 22, 2018, 07:12:05 pm »
Leo, are you planning on another batch of the ones with BNC connector? If not I'll definitely be getting one of the SMA's, but I'd prefer the BNC. Thanks in adv.
 

Offline KrudyZ

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Re: Yet another fast edge pulse generator
« Reply #367 on: May 22, 2018, 07:19:22 pm »
I just measured my  newly arrived MSOX3104T purchased from Keysight  "slightly used" via the webstore.  This came with fresh cal, all accessories and a 3 year warranty.  It was *not* cheap.

Measured rise time is 436 pS  which works out to 802.7 MHz  :-( 

I went to the datasheet and checked.  The spec is 1 GHz and rise time of <450 pS.  The 500 MHz version has a 700 pS risetime listed.   I'm deeply disappointed in Keysight fudging a specification like that.  It doesn't really matter for what I expect to do.

Well, 436 ps is less than the guaranteed 450 ps.
The 1 GHz spec is measured with a leveled signal generator and means that the displayed trace is less than 3 db down from the actual level at 1 GHz.
The formula that rise time (in ps) = 0.35 * bandwidth (in MHz) is not necessarily valid for modern scopes as it depends on the anti-aliasing filter used.
High end scopes even have selectable filters depending on the desired use case.
 

Offline KE5FX

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Re: Yet another fast edge pulse generator
« Reply #368 on: May 22, 2018, 07:36:31 pm »
Yeah, that 0.35 * Tr equation is only a general guideline.  It has a lot of assumptions baked into it that won't necessarily apply to a specific instrument.  As long as it meets the stated specs, you're fine.
 

Offline Converter

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Re: Yet another fast edge pulse generator
« Reply #369 on: May 22, 2018, 07:37:46 pm »

Well, 436 ps is less than the guaranteed 450 ps.
The 1 GHz spec is measured with a leveled signal generator and means that the displayed trace is less than 3 db down from the actual level at 1 GHz.
The formula that rise time (in ps) = 0.35 * bandwidth (in MHz) is not necessarily valid for modern scopes as it depends on the anti-aliasing filter used.
High end scopes even have selectable filters depending on the desired use case.
Absolutely right.
 

Offline Leo Bodnar

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Re: Yet another fast edge pulse generator
« Reply #370 on: May 22, 2018, 07:55:28 pm »
Hey Gerry,
I will make another batch of BNC ones this week and will drop you a PM.
Cheers
Leo
Leo, are you planning on another batch of the ones with BNC connector? If not I'll definitely be getting one of the SMA's, but I'd prefer the BNC. Thanks in adv.
 
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Offline HighVoltage

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Re: Yet another fast edge pulse generator
« Reply #371 on: May 22, 2018, 09:04:24 pm »
I just measured my  newly arrived MSOX3104T purchased from Keysight  "slightly used" via the webstore.  This came with fresh cal, all accessories and a 3 year warranty.  It was *not* cheap.

Measured rise time is 436 pS  which works out to 802.7 MHz  :-( 

I went to the datasheet and checked.  The spec is 1 GHz and rise time of <450 pS.  The 500 MHz version has a 700 pS risetime listed.   I'm deeply disappointed in Keysight fudging a specification like that.  It doesn't really matter for what I expect to do.
Don't be disappointed, your figure of 436ps is about the same, as what I measured on my MSOX3104A
Mean:    422 ps
Min:       400 ps
Max:      450 ps
StdDev: 9.37 ps
There are 3 kinds of people in this world, those who can count and those who can not.
 

Offline rhb

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Re: Yet another fast edge pulse generator
« Reply #372 on: May 22, 2018, 11:06:07 pm »
I'm not at *all* unhappy with the instrument.  It's *really* nice.   I'm unhappy with marketing.  The rise time is specified as "calculated"  in the datasheet and the conventional 0.35/BW rise time is listed.  But rather clearly the MSOX3104 rise time specification is measured.  Were it calculated, it would be <350 pS.

Using my out of cal 8648C at -20 dBm it appears to be down about 2 dB at 1 GHz.  I've got a 438A with 8481D and 8482A heads which have fresh cals with data, so I'll know more once I retrieve the cal data from Keysight and start testing everything I have against everything else I have.

I had planned on selling my Instek MSO2204EA, but I may reconsider as it will do much longer FFTs.  That decision will take some study as I have an 8560A with TG.  So I need to come up with some torture tests.

I always have found the 0.35/RT bit rather suspect as it makes a lot of assumptions about the rate at which the BW falls off.
 

Offline KE5FX

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Re: Yet another fast edge pulse generator
« Reply #373 on: May 22, 2018, 11:36:19 pm »
I'm not at *all* unhappy with the instrument.  It's *really* nice.   I'm unhappy with marketing.  The rise time is specified as "calculated"  in the datasheet and the conventional 0.35/BW rise time is listed.  But rather clearly the MSOX3104 rise time specification is measured.  Were it calculated, it would be <350 pS.

The 0.35/BW rise time equation is a loose approximation that's based on a specific filter response, which itself is a tradeoff between edge fidelity and raw 3-dB bandwidth.  Not all scopes are purely Gaussian. 



(from http://literature.cdn.keysight.com/litweb/pdf/5988-8008EN.pdf)

You're fine.  Nobody is trying to put one over on you.   :)
 

Offline rhb

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Re: Yet another fast edge pulse generator
« Reply #374 on: May 23, 2018, 12:47:27 am »
I'm not at *all* unhappy with the instrument.  It's *really* nice.   I'm unhappy with marketing.  The rise time is specified as "calculated"  in the datasheet and the conventional 0.35/BW rise time is listed.  But rather clearly the MSOX3104 rise time specification is measured.  Were it calculated, it would be <350 pS.

The 0.35/BW rise time equation is a loose approximation that's based on a specific filter response, which itself is a tradeoff between edge fidelity and raw 3-dB bandwidth.  Not all scopes are purely Gaussian. 



(from http://literature.cdn.keysight.com/litweb/pdf/5988-8008EN.pdf)

You're fine.  Nobody is trying to put one over on you.   :)

I'd prefer the Gaussian step response.  But I've not observed that to be an option except for R&S.  I can't see any reason that you could not let the user choose the step response.

My complaint is changing the method of calculation of rise time between models in the same line of instruments. It's a matter of integrity, not the performance of the instrument that bothers me.  The closest analogy I can think of is finding out your wife of 20 years is cheating on you.
 


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