Rigol's view on RTB2000 - Page 1
Forum section: electronics / testgear

author: ivonenand
author_rank: Contributor
timestamp: April 30, 2019, 04:27:22 am
content: Hi guys,I was just browsing through the reviews of the Rigol's MSO5000 on youtube and I stumbled upon this video:Here Rigol compares it's oscilloscope with the RTB2000, where they compare small signal analysis. Is this video something to be believed (let's leave behind the fact that the intent of the video in competition bashing)? I have high doubts that the 8-bit ADC and the 1-2mV/div digital zoom in the Rigol beats the true 1mV/div and 10-bit ADC in the RTB2000.Regards,Ivo

author: DaJMasta
author_rank: Super Contributor
timestamp: April 30, 2019, 05:07:46 am
content: That's really misleading. The R&S is clearly not interpolating correctly, for whatever reason, I'd suspect a firmware bug because those artifacts aren't present at the initial zoom levels and aren't possible waveforms with sin(x)/x interpolation being used. You can also tell that the Rigol's noise floor is higher, even though it doesn't have the same artifacting when zoomed in.It probably is an accurate representation of the firmware used, but it doesn't reflect the actual architecture performance, and it doesn't support a claim that the Rigol has more dynamic range or a lower noise floor, also the Rigol seems to be reporting its eres sample rate strangely... maybe it is still 2GS/s because it turns on the full 8GS/s before averaging kicks in to maintain the same rate.

author: 2N3055
author_rank: Super Contributor
timestamp: April 30, 2019, 05:09:38 am
content: In this case it does.This shows how you need to know limits of your instrument.They used signal that spans from +2V to -0,4V.Then they offset it and go to 20 mV/div.Top of the signal then overdrives input range of RTB2000 that has quite bad recovery from overdrive (it has been shown, RTM3000 also has recovery artefacts) and it distorts bottom of the signal it is showing. At 100 mV/div signal is still perfect. But at the 20 mV/div it distorts badly.MSO5000 seems to have either better dynamic range (so it doesn't distort yet at same settings) or much better overdrive recovery (they seem to claim that they have very good recovery compared to other scopes) so even on 10 mV/div it doesn't distort. At that level it still shows full res, until you get to 5 mV/dir it is not digitally zooming anything.So for this particular case, and by using both scopes the same way Rigol wins.Fact is that because of 10bit converters, you could actually use RTB2000 at 100 mV/div and than use zoom (digital zoom with finger) to see same signal without distortion. So you could see same thing by using scopes differently,each to it's own strength.This also show how "cheap" manufacturers can make things that are in fact better at some corner cases, and also that because it is expensive RTB2000 it doesn't mean that is superior in every case.Also it shows how most people misuse DC offset function. It's purpose is to offset constant DC offset form a complex signal so, for instance, you could look at milivolt level noise on top of of DC power bus or something. It is not vertical position button as we are using it most of the time. Also, because of limited dynamic range, you can't actually look at mV level noise on top of 5V bus because you don't have so much offset range usually. For that you'll have to AC couple the chanel. So offset is not so useful as you would think.

author: Aidanator7000
author_rank: Contributor
timestamp: April 30, 2019, 06:08:21 am
content: Quote from: 2N3055 on April 30, 2019, 05:09:38 amSorry to derail the thread a little, but:What is the point in the offset voltage when you can AC couple a signal?I been reading up the manual while waiting for my first scope to arrive, and I cannot think of a case where an offset voltage needs to be used instead of AC coupling.I'll probably figure it out once I start playing around, but thought i'd ask.

author: JPortici
author_rank: Super Contributor
timestamp: April 30, 2019, 06:21:35 am
content: well for one AC coupling isn't instantaneous. It may help if you have sufficiently high frequency AC imposed on a DC bus, but if you have AC on AC or slow AC over DC it will only distort the waveform

author: nctnico
author_rank: Super Contributor
timestamp: April 30, 2019, 10:31:20 am
content: Quote from: ivonenand on April 30, 2019, 04:27:22 amThis video has been linked to before. It is only showing the overdrive recovery of Rigol is better (but that may depend on the particular V/div setting). The RTB2000 is very likely to show the signal with much more detail compared to the MSO5000 because it has more resolution to start with. The creator of the video probably found that out too and decided to take a turn into a different subject: overdrive recovery.

author: genghisnico13
author_rank: Regular Contributor
timestamp: April 30, 2019, 02:35:59 pm
content: I don't have that exact same waveform, but I tried to replicate it with the integrated generator (not ARB, only with integrated waveforms) and I this is what I get.edit: added where last 2 pictures showing at what point it starts to show the undershootedit2: added the last picture showing 100mVdiv acquired waveform zoomed to 10mVdiv

author: JPortici
author_rank: Super Contributor
timestamp: April 30, 2019, 03:52:13 pm
content: Still, that's not an issue because you are overloading the input. some front ends will be better than others (more dynamic range and/or faster recovery) but this is user error, plain and simple.At least the scope is signaling an overload (Vpp clipping)Try and do that with the 50 ohm inputs and consider yourself lucky if you don't destroy them.