Beginner Questions on Cleverscope Resolution

Beginner Questions on Cleverscope Resolution, a forum discussion on Cleverscope. Join us for more discussions on Beginner Questions on Cleverscope Resolution on our Questions forum.

Back to Forum Index : Back to Questions   RSS

26 Jul 2007
Posts:

Hi! I'm a beginner, and I'm looking to purchase an MSO that will carry me through for a while (not just for the learning stage). At the moment, Cleverscope is at the top of my list - but even after reading the Performance document and other literature, there is still some ambiguity for me (at least for what I understand at the moment).

Given Cleverscope's options of 10-14 bit resolution, I understand the advantages of having 14 bit resolution over 10. What I'm not clear on is what the *disadvantages* are, and whether they cause the lower resolution versions to be more desireable - or whether the 14 bit version is still more desireable *despite* those disadvantages.

Can someone enlighten me? Thanks! :)

26 Jul 2007
Posts: 395

Hello Muse. Thanks for the question.
There are two disadvantages to having the 14 bit resolution version. They are cost (your problem, not ours!), and that when working in 14 bit mode, you lose (currently) 4 of the digital inputs (Inputs 4-7). That is because we only have a 32 bit wide sample word, into which we always pack the incoming sample data. With 2 x 14 bit you get 28 bits, leaving only 4 for the digitals.

It's for that reason that we allow the user to select the resolution used (in the Settings/Acquisition settings dialog). This means that if you buy a 14 bit digitizer, you can set it to 12 bit when you want all 8 digital inputs. (And you can set it to 10 bits, when you want to log the external trigger input, and the rear digital input as well). Hope this helps.

Eventually, when we get time, we are going to make the packing system (which works at 100 MSa/sec) be a bit more intelligent, so you don't have these losses.

26 Jul 2007
Posts:

BartSchroder said...
Hello Muse. Thanks for the question.
There are two disadvantages to having the 14 bit resolution version. They are cost (your problem, not ours!), and that when working in 14 bit mode, you lose (currently) 4 of the digital inputs (Inputs 4-7). That is because we only have a 32 bit wide sample word, into which we always pack the incoming sample data. With 2 x 14 bit you get 28 bits, leaving only 4 for the digitals.

It's for that reason that we allow the user to select the resolution used (in the Settings/Acquisition settings dialog). This means that if you buy a 14 bit digitizer, you can set it to 12 bit when you want all 8 digital inputs. (And you can set it to 10 bits, when you want to log the external trigger input, and the rear digital input as well). Hope this helps.

Eventually, when we get time, we are going to make the packing system (which works at 100 MSa/sec) be a bit more intelligent, so you don't have these losses.

Thank you for that clarification!

Incidentally, did I read the Performance document correctly that there was an additional disadvantage of 14 bit resolution, which was that you couldn't read as low a signal as you could in 10 bit mode? And if that is the case, would I be able to regain that ability by configuring the 14 bit digitizer for 10 bit mode? Or is that a nonchangeable limitation in the hardware?

27 Jul 2007
Posts: 395

Hello Muse,
Actually you can use the 14 bit digitizer over exactly the same range as the 10 bit digitizer, but when the signal you measure is noise floor limited you will not be getting the full 14 bit's resolution. Reading the performance document, the 10 bit noise limited signal level is 12 mV, so if you read a 12 mV signal with the 14 bit digitizer you will only be getting 10 bit performance, because the rest of the signal is below the noise floor (unless you average!). (And hey - that's still better than all those 8 bit scopes out there!).

27 Jul 2007
Posts:

BartSchroder said...
Hello Muse,
Actually you can use the 14 bit digitizer over exactly the same range as the 10 bit digitizer, but when the signal you measure is noise floor limited you will not be getting the full 14 bit's resolution. Reading the performance document, the 10 bit noise limited signal level is 12 mV, so if you read a 12 mV signal with the 14 bit digitizer you will only be getting 10 bit performance, because the rest of the signal is below the noise floor (unless you average!). (And hey - that's still better than all those 8 bit scopes out there!).

Excellent!

On a seperate note, I've looked over the specs, but it seems like every spec I've come across that deals with bandwidth is conditional (such and such bandwidth IF you use interpolation, or averaging, or filtering, etc...).

Can you tell me what the actual raw realtime bandwidth is for this scope?

28 Jul 2007
Posts: 395

Sorry Muse, its a conditional world!
The actual analog bandwidth of the scope is 100 MHz. However, we only sample at 100 MSa/sec. So we only have a real-time displayable bandwidth of about 20 Mhz. However you can use repetitive sampling (in which many samples are taken over hundreds or thousands of signal cycles and then merged to give the response over one cycle) to look at repetitive signals with the 100 Mhz analog bandwidth. Some other PC scopes give their primary sample rate as 5 GSa/sec, when in fact that's the repetitive rate, and the actual real time sample rate is much less. Some other scopes with short (eg 2500 or 3000 sample) buffers also claim 1 GSa/sec sampling, but this drops rapidly as the secs/division increases. For example a Tek TDS2000 series scope has the same sample rate as a Cleverscope at 2.5 usec/div. When operating at longer than 2.5 usecs/div the Cleverscope samples faster. If you want to look at single shot 2ns rise signals, Cleverscope is not for you. But if you want to explore a 20 msec SPI sequence or switchmode PWM sequence with 10ns resolution, Cleverscope will do the job. Finally you will not find any mainstream scopes with 14 bit (or even 12 bit) dynamic range. Hope this helps.

2 Aug 2007
Posts:

BartSchroder said...
Sorry Muse, its a conditional world!
The actual analog bandwidth of the scope is 100 MHz. However, we only sample at 100 MSa/sec. So we only have a real-time displayable bandwidth of about 20 Mhz. However you can use repetitive sampling (in which many samples are taken over hundreds or thousands of signal cycles and then merged to give the response over one cycle) to look at repetitive signals with the 100 Mhz analog bandwidth. Some other PC scopes give their primary sample rate as 5 GSa/sec, when in fact that's the repetitive rate, and the actual real time sample rate is much less. Some other scopes with short (eg 2500 or 3000 sample) buffers also claim 1 GSa/sec sampling, but this drops rapidly as the secs/division increases. For example a Tek TDS2000 series scope has the same sample rate as a Cleverscope at 2.5 usec/div. When operating at longer than 2.5 usecs/div the Cleverscope samples faster. If you want to look at single shot 2ns rise signals, Cleverscope is not for you. But if you want to explore a 20 msec SPI sequence or switchmode PWM sequence with 10ns resolution, Cleverscope will do the job. Finally you will not find any mainstream scopes with 14 bit (or even 12 bit) dynamic range. Hope this helps.

It most definitely does - thank you for explaining! :)
Back to Forum Index : Back to Questions   RSS
You must be logged in to post a reply



You need to Register or Log In before posting on these forums.

×

Your shopping cart is empty.