Author Topic: Pretty scope pictures  (Read 3819 times)

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Offline tntTopic starter

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Pretty scope pictures
« on: April 27, 2011, 07:58:11 pm »
Hi,

I wanted to post a few nice pictures just for fun and also to remind that what you use to probe can be very important.

The signal in question is a USB 2.0 hi-speed IDLE packet between my laptop and a USB stick. It's being probed at the usb stick end, after a usb extender cable.

The equipment used is :
* DSO-X 3034A (350MHz)
* Passive probe N2890A 10:1 500MHz 10Mohm 11pf
* Active probe 1158A 10:1 4GHz 100k 0.8pf

First a reminder of how ground connection matter !
Both captures are with a passive probe, the first one using the normal ground lead/alligator and the second one uses the ground 'spring' to have a very short connection.



Then a few close up shots comparing the passive (on the left) and active probe (on the right):




As you can see it doesn't seem to actually make that much of a difference in this case. The eye seems smaller with the active one but I think it's actually closer to the truth, it is also less "woobly" that with the passive probe (flatter top, less ringing).


If you have cool pictures of nice measurements, please post them :p
 

Offline Leo Bodnar

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Re: Pretty scope pictures
« Reply #1 on: April 28, 2011, 11:45:30 am »
The signal in question is a USB 2.0 hi-speed IDLE packet between my laptop and a USB stick. It's being probed at the usb stick end, after a usb extender cable.
Extender cable is USB-illegal so you results are not comprehensive ;D
 

alm

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Re: Pretty scope pictures
« Reply #2 on: April 30, 2011, 02:04:59 pm »
As you can see it doesn't seem to actually make that much of a difference in this case. The eye seems smaller with the active one but I think it's actually closer to the truth, it is also less "woobly" that with the passive probe (flatter top, less ringing).
The difference between active and passive probes would probably be much larger with a longer ground lead. Because of the lower input capacitance of active probes, the inductance of the ground lead is much less significant. It would also be larger with a high source impedance, since the high input capacitance of passive probes represents a very low impedance at high frequencies (see the input impedance vs frequency graph in the data sheet).
 

Offline tntTopic starter

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Re: Pretty scope pictures
« Reply #3 on: May 02, 2011, 06:06:22 pm »
Yes that's true.

Actually they do put that in the "feature" list : "signal browsing". You can just have a long lead and view fairly ok signal up to a few hundred MHz without issues. For AC signals like oscillators and such, NO ground connection at all even works pretty well if you just want to have an idea of what you're probing :) (obviously the DC components is not there ...).
 


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