There is a common myth that has been propagated around here that the input stages on digital scopes are inherently noisier than analog scopes. While I have known that this isn't true, I have not found a great comprehensive source on why this is so. Dave Jones over at EEVBlog just did a two part series(actually three if you count the episode that started this) on this topic. It's a must watch for anyone who works with circuits. He explains how sampling technology picks up and reveals noise/signal that an analog scope will hide. The effect of memory depth on the illusion of noise. The effect of scope bandwidth on noise. He also discusses the advantages to the analog method as well as the digital method. Explains the logic behind technologies like Digital Phosphor (aka Intensity Gradient, Variable Intensity, etc.). It's a really good comprehensive primer into noise and oscilloscopes; a must watch for anyone working with circuits.
Part 1:
https://www.youtube.com/watch?v=Znwp0pK8Tzk
Part 2:
EEVblog #610 - Why Digital Scopes Appear Noisy - Part 2 - Page 1
Part 1:
https://www.youtube.com/watch?v=Znwp0pK8Tzk
Part 2:
EEVblog #610 - Why Digital Scopes Appear Noisy - Part 2 - Page 1
I don't know, but suspect that a) for most people the residual noise of a good analog scope is a non-issue, and b) that for the most part a top quality used analog scope is as good or better than a cheap digital scope in that department.
I suspect that the high quality new Agilent, Tek and other top brand digital scopes are tremendously good instruments.
_-_-
I suspect that the high quality new Agilent, Tek and other top brand digital scopes are tremendously good instruments.
_-_-
At least one of the early digital oscilloscopes had terrible inter channel cross-talk. I can't remember which model. With all the switch mode power supplies and processors in the digital Oscilloscopes they may have been circumstances with some models when the noise was worse than an analogue one. So I think that the myth had a grain of truth. Not generally true today though.
I don't think I made myself clear enough earlier. I am not attempting to say that analog scopes are bad. Just trying to clear up some misinformation I commonly see spouted about digital scopes being noisy.
I think each has its benefits. An analog helps you see the "real" signal better without the noise. Pure digital scopes show you the "true" signal with the real noise thrown in which can sometimes obscure the "real" signal. DPO type scopes try to bridge both giving you both types of information at once. That being said, if you get a low-end scope from one of the more reputable manufacturers (Rigol, some Siglents, etc) then you will have a scope on par or significantly better than old top-end analog scopes. I often cite the Rigol DS1074Z, it has DPO functionality, ability to decode digital data, plus lots of other stuff. In my opinion putting it at least on par with the old Tek 24xx series scopes and for $500-600 new. If you don't go with a reputable manufacturer then I would agree (Owon for example). The market has changed dramatically in the past few years. 4-5 years ago I would have agreed whole-heartedly that one of the old Tek scopes is a better value. Now the bottom line is really putting some downwards pressure on the old analog scopes.
As for a top-end new scope, no doubt they are AMAZING instruments. It's really a golden era of scopes we have entered. There is true market pressure across the board which have made available to hobbyists stuff they could only dream of a decade ago. Agilent recently had a deal one their DSO-X scopes where if you purchased a single option they gave you ALL of the other options for free. This is in direct response to encroachment in performance by companies like Rigol (and Tek to a much lesser degree).
My digital scope (LeCroy WaveAce 214) has a 2mV scale. Some go even lower. The Rigol DS1074Z/DS1104Z (which should not be confused with the DS1052/DS1102 series as they are 100% different) has resolution all the way down to 500uV/div.
Yeah that might have been, the early era of digital scopes was an interesting place filled with loads of compromises and strange choices. Plus people not quite sure what they were doing. Just look at the old Nicolet digital scopes. THose are interesting beasts. Some are high precision scopes, the likes you barely see even today. Just they had really low frequency ranges, I'm guessing they were intended more for physics labs than electronics labs.
The point that Dave makes is that the noise you can clearly see in a digital scope is HIDDEN by the analog scope because of our persistence of vision. He's saying that what looks like a crystal clear sharp trace on an analog scope can actually hide a lot of signal if its very high frequency because of persistence of vision.
I think each has its benefits. An analog helps you see the "real" signal better without the noise. Pure digital scopes show you the "true" signal with the real noise thrown in which can sometimes obscure the "real" signal. DPO type scopes try to bridge both giving you both types of information at once. That being said, if you get a low-end scope from one of the more reputable manufacturers (Rigol, some Siglents, etc) then you will have a scope on par or significantly better than old top-end analog scopes. I often cite the Rigol DS1074Z, it has DPO functionality, ability to decode digital data, plus lots of other stuff. In my opinion putting it at least on par with the old Tek 24xx series scopes and for $500-600 new. If you don't go with a reputable manufacturer then I would agree (Owon for example). The market has changed dramatically in the past few years. 4-5 years ago I would have agreed whole-heartedly that one of the old Tek scopes is a better value. Now the bottom line is really putting some downwards pressure on the old analog scopes.
As for a top-end new scope, no doubt they are AMAZING instruments. It's really a golden era of scopes we have entered. There is true market pressure across the board which have made available to hobbyists stuff they could only dream of a decade ago. Agilent recently had a deal one their DSO-X scopes where if you purchased a single option they gave you ALL of the other options for free. This is in direct response to encroachment in performance by companies like Rigol (and Tek to a much lesser degree).
I think that is one of the points her tries to illustrate so you hit the nose on the head. About the dependence on bandwidth and noise.What might be happening is an analog 20MHz scope (that has (and can use) a 2mV/div scale ) is being compared to a 500MHz digital scope ( that usually has a 5mV/div scale).
The wider bandwidth may contain LESS noise per root Hz but cannot demonstrate that.
Just a thought.
My digital scope (LeCroy WaveAce 214) has a 2mV scale. Some go even lower. The Rigol DS1074Z/DS1104Z (which should not be confused with the DS1052/DS1102 series as they are 100% different) has resolution all the way down to 500uV/div.
Yeah that might have been, the early era of digital scopes was an interesting place filled with loads of compromises and strange choices. Plus people not quite sure what they were doing. Just look at the old Nicolet digital scopes. THose are interesting beasts. Some are high precision scopes, the likes you barely see even today. Just they had really low frequency ranges, I'm guessing they were intended more for physics labs than electronics labs.
Digital scopes have averaging function to remove the noise from the display
The biggest benefit of a digital scope over analog is you can take screen shots more easily
.
Pre-triggering is the second.
The biggest benefit of a digital scope over analog is you can take screen shots more easily
Getting this rectifier ringing shot took less than 1 minute of work. No cheating, the probe is on the transformer secondary, and the scope is set to line trigger. I would like to see similar screenshot on analog scope. Last time I tried, it was not so easy...
While most do, it has to be manually enabled. It is NOT on by default. On my LeCroy you have to enable Averaging mode and select the number of runs to average. Clearly, you didn't watch the videos if you can't see any additional benefits to digital over analog. Let alone the ones mentioned by others here.Digital scopes have averaging function to remove the noise from the display
The biggest benefit of a digital scope over analog is you can take screen shots more easily
.
I'll add a few more:
1) Decoding - many of the modern digital scopes will decode basic data protocols like I2C, SPI, UART, CAN etc.
2) Triggering: the ability to trigger on highly specific conditions (including triggering off of decode, multiple parameter triggering etc.).
3) Long storage memories: The large storage memories available now allow for you to record LOADS of waveforms and find specific troublesome ones that you would not be able to spot with an analog scope.
4) Real signal: Because of the persistence of vision and ability to discern contrast is limited, analog scopes will often hide parts of the real signal. Small seldomly occuring glitches can be obscured. In a digital scope thats not an issue and with the DPO scopes you not only can see the real signal but see a better image of what the whole signal looks like.
5) Ability to zoom and pan around.
Thats not to say there aren't advantages to analog scopes, just that they are getting fewer and fewer as time goes on.
Last edited:
OK, maybe I cheated a little. The scope isn't actually triggered by the event that is observed.
First I adjusted the vertical offset and volts/div to get the interesting bits on screen as you'd expect (this scope has a rather large DC offset adjustment range, which is nice, and the overload recovery time after the "trace" has gone offscreen is specified too). Then with a half-period on the screen (10 ms) I just pushed Record button. This thing will record millions of samples at 1-2 Gsps, so after that, no problem to zoom in on the interesting part and take a shot. That's why it is simply set on "AC line" trigger. The whole operation takes less time than to write this paragraph...
DS2072 is a really nice scope, especially with the full options hack...
My old analog scope also was really nice, but it died. Honestly the new breed of digital scopes with intensity grating and fast update are almost as good as the analog ones, with all the advantages of digital. Not the same feeling, though.
First I adjusted the vertical offset and volts/div to get the interesting bits on screen as you'd expect (this scope has a rather large DC offset adjustment range, which is nice, and the overload recovery time after the "trace" has gone offscreen is specified too). Then with a half-period on the screen (10 ms) I just pushed Record button. This thing will record millions of samples at 1-2 Gsps, so after that, no problem to zoom in on the interesting part and take a shot. That's why it is simply set on "AC line" trigger. The whole operation takes less time than to write this paragraph...
DS2072 is a really nice scope, especially with the full options hack...
My old analog scope also was really nice, but it died. Honestly the new breed of digital scopes with intensity grating and fast update are almost as good as the analog ones, with all the advantages of digital. Not the same feeling, though.
Last edited:
Rectifier ringing, measured with Tektronix 2245A. I should have increased the sensitivity for greater resolution...
And no aliasing artifacts
But, as said, a digital scope brings so much convenience in usage. A new digital scope is on my purchase list.
Peufeu, what kind of Rigol scope in your screenshot?
Edit: DS2072 I presume.
Last edited:
Roll mode..
In the late 1990s I purchased a then 9yr old HP54111D, which was a fairly early 4 channel HP digital scope that unfortunately had serious quantization artifacts, but was very convenient for looking at logic where timing relationships and easy storage and analysis were important. It did not do a good job even with high amplitude repetitive sine waves. (Can't remember if it had averaging, if it did I certainly tried it) I did not keep it for very long, and sold it for about what I paid for it.
I plan to eventually acquire a Tek TBS series digital scope or something similar at some point to complement my 2245A.
In the late 1990s I purchased a then 9yr old HP54111D, which was a fairly early 4 channel HP digital scope that unfortunately had serious quantization artifacts, but was very convenient for looking at logic where timing relationships and easy storage and analysis were important. It did not do a good job even with high amplitude repetitive sine waves. (Can't remember if it had averaging, if it did I certainly tried it) I did not keep it for very long, and sold it for about what I paid for it.
I plan to eventually acquire a Tek TBS series digital scope or something similar at some point to complement my 2245A.
Roll mode..
Are you referring to my screenshot? It's sync!
I plan buying an DS1104Z but maybe I fool myself? Rigol 2000 series are of course much better but is the additional cost worth it? I like low input noise any maybe the cheap ones do not perform in this regard.
Intensity grading comparison, twice Rigol and one Agilent: Intensity Grading Comparison
Nice !
Yes it is a DS2072A hacked to DS2302A (300 MHz bandwidth)... you could hack the non-A models to 200MHz.
> Rigol 2000 series are of course much better (than DS1104Z) but is the additional cost worth it?
Actually DS2072 and DS1104Z cost does not seem very different. DS1104Z looks very much like DS2000 on the video, all on-screen stuff seems identical too...
If you refer to older cheaper DS1052 that started it all, of course the 2000 is better in every possible way and the price difference is really justified.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.