Scope probes as supplied by Rigol for the low end scopes, a discussion.

[phenol]

For those who really really need to see it 

Question is about the rise time of the function generator source. If the rise time of the source is limited (which I see in the AWG datasheet as 8ns) then of course the performance of the two probes will be identical - they have 2.3ns and 0.9ns respectively. You have to test them with rise time that is close to the rise time of the scope (which is 3.5ns) in order to see a difference.

The test with 8ns rise time pulse under these conditions is meaningless.?

also, nobody really cared to hook their funct generators directly to the scope bnc, terminate everything properly and then assess the contribution of the probe vs what the scope shows w/o it.
A simple circuit that can give <1ns rise time with low jitter could be a x-tal oscillator built around 74AC04 dead bug style on copper foil with ample decoupling of the VDD pin to ground. The spare inverters can be paralleled together to buffer the oscillator and provide really low output resistance.

[EEVblog]

Question is about the rise time of the function generator source. If the rise time of the source is limited (which I see in the AWG datasheet as 8ns) then of course the performance of the two probes will be identical - they have 2.3ns and 0.9ns respectively. You have to test them with rise time that is close to the rise time of the scope (which is 3.5ns) in order to see a difference.
The test with 8ns rise time pulse under these conditions is meaningless.?

No, it's not. The whole idea was to try and verify the gross irregularity that Lightages saw.


Note the 50ns/div timebase.
So 8ns risetime was plenty to confirm the problem. In fact it's about 3ns or so, take a look at my screen shots.

[TMM]

I think Lightages signal source might be at fault? That overshoot seems to be too low frequency to be directly caused by the scope/probes.

My main problem with Rigol's probes right now: I received my scope last week and one of the probe tips came off when I removed the hook attachment for the second or third time.

Wow, never had that before and i've owned 6 of the RP2200 probes. The ones that were supplied with the DS1054Z do seem to be slightly lower quality than the ones that came with a DS1052E - the plastic casing just feels cheaper and the hooks are a little more rounded so they fall off (unclip) easier (though, the older ones weren't much better). I can't understand why they can't make the probe hooks as sharp as the cheap P6100 chinese probes you can get from ebay/etc.

[Lightages]

I will say it again. The overshoot is not the probes. The waveform actually has this ringing. The loading of the source by the probes have nothing to do with the difference because they are both connected at the same time.

I have a Siglent SDG1025 almost in my hands. I will do another test with a more proper source properly loaded and we will see if I can detect any difference.

[Lightages]

DS2072A says scope input is 16pF. I measured almost 18.5pF @70MHz.

What instrument did you use for this test?

[Bud]

I'm not sure why you are rounding up. 18.447pf rounded to one decimal point should be 18.4pf or 18.45pf if using 2 decimal places

First, i said "almost 18.5". Second, i am not a programmer and i live in a real world. Try paying for you morning coffee using your rules and see how much that guy/girl at the cash counter agree with you.

, yeah picky but we all know how you feel about Rigol

Oh thank you for the recognition of my humble efforts. Yes i am not OK with companies that have no idea what they are doing.

[tautech]

I will say it again. The overshoot is not the probes. The waveform actually has this ringing. The loading of the source by the probes have nothing to do with the difference because they are both connected at the same time.

I have a Siglent SDG1025 almost in my hands. I will do another test with a more proper source properly loaded and we will see if I can detect any difference.

Check this thread for a REAL comparison:https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg590683/#msg590683
Siglent SDG1025 & SDS1072CML.

[pickle9000]

I will say it again. The overshoot is not the probes. The waveform actually has this ringing. The loading of the source by the probes have nothing to do with the difference because they are both connected at the same time.

I have a Siglent SDG1025 almost in my hands. I will do another test with a more proper source properly loaded and we will see if I can detect any difference.

Check this thread for a REAL comparison:https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg590683/#msg590683
Siglent SDG1025 & SDS1072CML.

Very entertaining thread. https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg592378/#msg592378

[tautech]

I will say it again. The overshoot is not the probes. The waveform actually has this ringing. The loading of the source by the probes have nothing to do with the difference because they are both connected at the same time.

I have a Siglent SDG1025 almost in my hands. I will do another test with a more proper source properly loaded and we will see if I can detect any difference.

Check this thread for a REAL comparison:https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg590683/#msg590683
Siglent SDG1025 & SDS1072CML.

Very entertaining thread. https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg592378/#msg592378

And it's getting better: https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg592751/#msg592751

[miguelvp]

I will say it again. The overshoot is not the probes. The waveform actually has this ringing. The loading of the source by the probes have nothing to do with the difference because they are both connected at the same time.

I have a Siglent SDG1025 almost in my hands. I will do another test with a more proper source properly loaded and we will see if I can detect any difference.

Check this thread for a REAL comparison:https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg590683/#msg590683
Siglent SDG1025 & SDS1072CML.

Comparison of using a BNC instead of probes?

But the subject at hand is all about using probes, so not sure what you mean by a real comparison.

[tautech]

I will say it again. The overshoot is not the probes. The waveform actually has this ringing. The loading of the source by the probes have nothing to do with the difference because they are both connected at the same time.

I have a Siglent SDG1025 almost in my hands. I will do another test with a more proper source properly loaded and we will see if I can detect any difference.

Check this thread for a REAL comparison:https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg590683/#msg590683
Siglent SDG1025 & SDS1072CML.

Comparison of using a BNC instead of probes?

But the subject at hand is all about using probes, so not sure what you mean by a real comparison.

Ok, poorly put. 
But the fact of the matter is probes alone are not appropriate for accurate representaion of a waveform with a fast leading edge. Impedance matching is also very important.
The "show us your square wave" thread has many examples of connection (some on purpose) that display similar ringing to Lightages.

@Lightages
Are you using the SDG1025 with High Z or 50 Ohm output setting?
Probe to BNC adapter?

[Lightages]

It was described before but people seem to not be understanding the situation. Perhaps this is my fault so here it is again, in excruciating detail.

I am using an analog function generator that has a dedicated TTL output, not rated at 50ohm. I have a 50ohm terminator on one side of the T and a BNC coax on the other end. This gives a ringing square wave as the output. It is not meant to be a proper square wave. I was looking for the fastest rise time I could get from the output. It was just by accident that I arrived at this setup.

I am still waiting for my SDG1025 to arrive.

I have a DS1052E upgraded to 100MHz that came with RP3300 probes, old versions, that do not have a compensation adjustment at the BNC.

I have a DS1054Z upgraded to 100MHz that came with RP2200 probes.

I was casually comparing the performance of the two systems. When I started looking at the waveforms that were displayed on both scopes while probing the same signal I noticed that the DS1052E seemed to show more detail on the waveform than the DS1054Z. So thinking that perhaps the upgrade had not worked on the DS1054Z I started to investigate. After some poking around I swapped the probes from one scope to the next (after compensating of course) and the difference I observed moved with the probes.

Both RP3300 probes showed more detail on the waveform than the 4 RP2200 probes I have, and on either scope and on any of the channels. One RP2200 and one RP3300 probe were always connected at the same time to the signal so any difference in loading of the signal from the different probe model is a moot point. I have tried probing the source BNC directly with ground spring clips instead of the alligator clip leads, the same on the end of the original arrangement, at the T adapter, etc....

In each and every case, the same difference in the intentionally ringing waveform appeared. The RP3300 probes show more detail and higher peaks on the ringing than the RP2200, regardless of scope, channel and test method.

When calculated according to the formula presented on Dave's video, a theoretical 100MHz bandwidth scope with theoretical 150MHZ probe will have system bandwidth of around 84.2MHz. The same scope with a 350MHz probe will have a bandwidth of 96.2MHZ. With this in mind, it is a small leap to justify the difference I see with my different probes. It also shows that theoretically the probes limit the performance of the scope, whether it is normal practice to supply the same bandwidth probes for a scope or not.

It has now been demonstrated, at least in one person's case, that the DS1054Z upgraded to 100MHz actually seems to have a bandwidth of between 130MHz and 150MHz. With this in mind the difference I see in the waveform is even easier to rationalize. It is because this affects what effect the probes have on the bandwidth. It is a wider spread in the system bandwidth, namely 106MHZ  for the RP2200 vs 138MHz for the RP3300. This is assuming that the scope has 150MHz bandwidth.

So as far as I am concerned the difference that I see is easily explained by these last theoretical calculations and it answers my question about whether or not the probes as supplied affect the overall scope's performance. If the 100MHz bandwidth of the scope is assumed, or lower, then the probes will bring the overall system performance down below the rating of the scope. In the case of the 50MHz bandwidth model, down to a theoretical 44.7MHz. If the bandwidth of the 100MHz model scope is really closer to the 150MHz suggested by another person then the RP2200 probes bring the system bandwidth down to 106MHz and the probes do not affect the rated performance of the scope as a system with the probes.

Another conclusion can be reached to I think. If you do not want your scope measurement system to be degraded by the probes, they should have at least 3.5 times the bandwidth of the scope. At the very least you should be aware of the effects of the bandwidth of the probes in your overall system performance. The last sentence holds true for any system that all components need to be taken into account of course but I just wanted to complete the logical conclusion.

[Pjotr]

....................................
But the fact of the matter is probes alone are not appropriate for accurate representaion of a waveform with a fast leading edge. Impedance matching is also very important.
The "show us your square wave" thread has many examples of connection (some on purpose) that display similar ringing to Lightages.

Brings up also the question: What for are high impedance probes used? Certainly not for perfect pulse response at hundreds of MHz. For that you need other measures. Probing with high impedance probes is mostly done at places with strongly varying source impedances that are, most time, not taken into account. So you need to know not to expect the "perfect". And sometimes how the probe loading affects the DUT if that counts. It has its limits. Doesn't mean they may limit the bandwidth of scope or may have uneven frequency/phase response by itself. But most time the circuitry does it due to high impedances, especially with analogue circuitry "seen" by the probe.

[TMM]

It was described before but people seem to not be understanding the situation. Perhaps this is my fault so here it is again, in excruciating detail.

I am using an analog function generator that has a dedicated TTL output, not rated at 50ohm. I have a 50ohm terminator on one side of the T and a BNC coax on the other end. This gives a ringing square wave as the output. It is not meant to be a proper square wave. I was looking for the fastest rise time I could get from the output. It was just by accident that I arrived at this setup.

I am still waiting for my SDG1025 to arrive.

I have a DS1052E upgraded to 100MHz that came with RP3300 probes, old versions, that do not have a compensation adjustment at the BNC.

I have a DS1054Z upgraded to 100MHz that came with RP2200 probes.

I was casually comparing the performance of the two systems. When I started looking at the waveforms that were displayed on both scopes while probing the same signal I noticed that the DS1052E seemed to show more detail on the waveform than the DS1054Z. So thinking that perhaps the upgrade had not worked on the DS1054Z I started to investigate. After some poking around I swapped the probes from one scope to the next (after compensating of course) and the difference I observed moved with the probes.

Both RP3300 probes showed more detail on the waveform than the 4 RP2200 probes I have, and on either scope and on any of the channels. One RP2200 and one RP3300 probe were always connected at the same time to the signal so any difference in loading of the signal from the different probe model is a moot point. I have tried probing the source BNC directly with ground spring clips instead of the alligator clip leads, the same on the end of the original arrangement, at the T adapter, etc....

In each and every case, the same difference in the intentionally ringing waveform appeared. The RP3300 probes show more detail and higher peaks on the ringing than the RP2200, regardless of scope, channel and test method.

When calculated according to the formula presented on Dave's video, a theoretical 100MHz bandwidth scope with theoretical 150MHZ probe will have system bandwidth of around 84.2MHz. The same scope with a 350MHz probe will have a bandwidth of 96.2MHZ. With this in mind, it is a small leap to justify the difference I see with my different probes. It also shows that theoretically the probes limit the performance of the scope, whether it is normal practice to supply the same bandwidth probes for a scope or not.

It has now been demonstrated, at least in one person's case, that the DS1054Z upgraded to 100MHz actually seems to have a bandwidth of between 130MHz and 150MHz. With this in mind the difference I see in the waveform is even easier to rationalize. It is because this affects what effect the probes have on the bandwidth. It is a wider spread in the system bandwidth, namely 106MHZ  for the RP2200 vs 138MHz for the RP3300. This is assuming that the scope has 150MHz bandwidth.

So as far as I am concerned the difference that I see is easily explained by these last theoretical calculations and it answers my question about whether or not the probes as supplied affect the overall scope's performance.

The thing is, the 'ringing' in your signal is low enough in frequency that neither probe should change it's shape.

I've replicated your signal and compared it to a square wave (w/ similar rise time) and it's already pretty far down by 100MHz, so why are we seeing a difference between 150MHz and 350MHz probes, which should both be more or less completely flat to 100MHz? There should be very little change visible on an 8bit 'scope display when frequency components that are already 60dB down are further attenuated.

Time domain:


Freq domain (800KHz to 200MHz):


And here is a 2.5MHz square wave generated by a DG4062 and probed with a DS1054Z(100MHz) and RP2200 probe using alligator clip on the BNC of the function gen. As expected the ringing is much higher in frequency and significantly smaller in amplitude, consistent with frequency components >100MHz being attenuated and components <100MHz being more or less untouched.


Imo what you are observing is an effect of the difference in capacitive loading by each of the probes, not the difference in their inherent bandwidth (frequency response). You'd probably see the same <100MHz effect with a 500MHz probe or by adding a small capacitor.

[Lightages]

Imo what you are observing is an effect of the difference in capacitive loading by each of the probes, not the difference in their inherent bandwidth (frequency response). You'd probably see the same <100MHz effect with a 500MHz probe or by adding a small capacitor.

One RP2200 and one RP3300 probe were always connected at the same time to the signal so any difference in loading of the signal from the different probe model is a moot point.

I understand what you are trying to say and what you have tried to simulate. What appears in the waveform looks like 50MHz ringing. The fact is that there is a difference with the 350MHz probes vs the 150MHz probes with the same conditions. Please understand that both probes were connected at the same time, therefore no different loading seen, they were loading the source in parallel. The same difference in the displayed waveform exists if they are connected one at a time too.

I have no other explanation as of yet except the conclusion I have reached. I wish I had a better way to test the conclusion, but I don't.

I am letting this go until someone who has the right equipment to measure my probes definitively steps up and offers to test them. That would be getting a bit more anal than even I am being about this right now.

[TMM]

Remember that just because the voltage is the same at the probe tips doesn't mean the current (and phase of the current) going into each probe is the same. If one of the harmonic components is shifted in phase slightly it can cause a dramatic visual difference in the waveform.

[Lightages]

Yes, I understand that probes and their interactions are complex. The thing is that they display the same difference in the waveform respectively whether they are connected at the same time, separately, ground leads or ground clips, and connected directly to the source or through cables.

Without the right equipment there is no determining if what I see is the real performance of the probes or something else.

[bson]

In the case of the 50MHz bandwidth model, [the RP2200 brings it] down to a theoretical 44.7MHz.

Unless the 50MHz model is slightly over 50MHz and with the 150MHz probe ends up at the specified 50MHz.  In other words, maybe the bandwidth specification is the system bandwidth with the supplied probes.

[Lightages]

I just came to a stupidly obvious realization......   

Perhaps all my other probes are good and the two RP3300 probes I have are the incorrect ones. Perhaps this is why Rigol changed the probe design to the way they are now instead of the design that I have. Perhaps they realized that 300MHz was pushing envelope of the old design.  Remember that my RP3300 probes look identical to the RP2200 probes.

Sorry if this might have been an obvious thought to others, but when you get tunnel vision it can get really bad.

This makes more sense in light of the peakiness of the ringing at around 50MHz because this would be well within the bandwidth of any setup but faulty or badly designed probes could be peaky at that frequency.

[tggzzz]

Well I have measured with two scopes, all the available channels, with the cable from the function generator open ended alligator clips, 50 ohm load at the generator, at the end of a BNC terminated cable, with the spring clip ground point on the probes, directly into the function generator, and all the different arrangements that are possible. Yes the observed wave form changed, but there is always the same relative difference of the appearance of the wave form between the RP2200 and the RP3300.

I am either doing something wrong, ...

Yes, you are doing something wrong. There's absolutely no point in trying to measure bandwidth/risetimes with the ringing shown on your screen capture, since the parasitic components causing the ringing will define the circuit's response - and the probe+scope response will be irrelevant. So, what are those parasitic components?

In this and, as far as I can see subsequent notes, you have ignored one very important feature of your measurement: the wire associated with "cable from the function generator open ended alligator clips" and the wire associated with "spring clip ground point on the probes". Those wires are inductors, and they resonate with the probe tip capacitance to give the ringing overshoot in your screen capture.

I can't estimate the inductance introduced since you haven't specified how long the wires are, but online calculators will show that 10cm of wire has an inductance of around 100nH. Couple that with the probe tip capacitance and it is capable of explaining the waveforms seen.

The first step, as others have pointed out, is to get rid of the ringing by getting rid of the inductance, which means getting rid of the ground wires. Either connect directly, or use a short ground such as the bayonet ground illustrated below (a 6.5pF 500MHz probe).

Note that the probe's high frequency compensation is irrelevant to those effects.

[Lightages]

Thanks for the response tggzzz, but I think you missed that I probed directly at the BNC of the output on the generator too, and the the apparent difference between the probes was still there. I also said that I was trying to explain the difference I saw in the waveform, it was not to measure the rise time.

As I said in my last post, it seems more likely now that the RP3300 probes are either faulty or poorly designed. They have been the only probes that show this extra peakiness to the signal. All my other probes, RP2200 and some P6300? probes I just received, show the same waveform. This points to the RP3300 probes being the inaccurate ones. I made the assumption that the RP3300 probes would be better than the others and my logic or "illogic" flowed from that.

[markce]

Perhaps they realized that 300MHz was pushing envelope of the old design.

I've seen this done before. I've another probe where they stretched bandwidth from 75 to 100MHz which causes a slight peak in the response, but they documented it. As fa as I know, Rigol does not specify response flatness.

[blackdog]

Hi, 


I dit some testing with probes on my Rigol DS1104Z.

Yellow probe: Rogol RP2200, 150Mhz ~17pF
Pink probe: Picotech Type?, 60Mhz
Blue probe: Philips PM8935, 250Mhz ~11pF (0.8nS)

1Khz Generator = Hameg HMF2525, about 1.2V
First the pictures of the generator en the probe connectors


Frequentie setting.



First, remenber...
Yellow - Rigol
Pink - Picotech
Blue - Philips

1Khz 100usec settings on the Rigol DS1104 scoop



1Khz 5usec settings on the Rigol DS1104 scoop



1Khz 1usec settings on the Rigol DS1104 scoop



1Khz 100nsec settings on the Rigol DS1104 scoop



1Khz 20nsec settings on the Rigol DS1104 scoop



1Khz 5nsec settings on the Rigol DS1104 scoop



Anyone tried the Rigol RP2200 Probe? "Thats not so good Al..." (Weezer)
The difference in time, is due to the length of the probe cable.
I am not to happy about the RP2200 Probes...

Kind regarts,
Blackdog

[Pjotr]

You can't expect top notch performance from cheap probes that often use simple of the shelf coax. Normal coax will ring anyway when not properly terminated with its characteristic impedance. The better probes use "resistive" coax to damp the ringing.

B.t.w. you loaded the generator with 3 probes, that means a loading of about 45 - 50 pF. Given the Ri of the generator of 50 ohms, that limits your BW anyway to app. 70 MHZ or a rise time of about 5 - 6 nS. Using a 50 ohms feed-trough terminator reduces the source resistance to 25 ohms, speeding up the source 2x. With a faster rise time the RP2200 will probably ring a lot more.

[blackdog]

Hi Pjotr,

Do you realy think i'am not aware about the loading of the generator?
I dit a test whit 3 different probes, one slower than de Rigol, one faster than the Rigol.
Both beat the crap out of the Rigol Probe, look at the pictures, there is a lot of oveshoot whit the Rigol probe...

Its all about the difference between the probes...
And the probe's were all measurd at the same time.

Kind regarts,
Blackdog