Products > Test Equipment
REVIEW - Rigol DS2072 - First Impressions of the DS2000 series from Rigol
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marmad:

--- Quote from: Galaxyrise on November 17, 2013, 07:50:13 am ---See that the sample rate is 1Gsa/s in my screenshot, which should leave plenty of effective sample rate for a 100kHz signal.

--- End quote ---
@Galaxyrise: Interestingly, the reason the 100kHz signal is so attenuated in the image you posted is that it falls almost directly in the first null point of the stopband @ 1ms/div (see image above which shows the null points of an averaging filter). Compare it to this image using the same settings as you, but with a 150kHz sine wave - which falls beyond the first null point (although still attenuated by -12dB):



Playing around with sending sweeps to the Rigol while in High Res mode reveal the nulls that exist in the stopband at each time base setting (while using 14MB/AUTO mem depth). These null points are at the averaging frequency (sample rate/number of samples averaged) and its harmonics.

Bandwidths @ 14MB/AUTO memory depth in High Res mode on DS2000

Time base  - Bandwidth (-3db)  - First null in stopband 10ms/div~4.3kHz~10kHz5ms/div~8.6kHz~20kHz2ms/div~21.6kHz~50kHz1ms/div~43.3kHz~100kHz500us/div~86.6kHz~200kHz200us/div~173.2kHz~400kHz100us/div~346.4kHz~800kHz50us/div~692.8kHz~1.6MHz20us/div~1.38MHz~3.2MHz10us/div~2.77MHz~6.4MHz5us/div~5.54MHz~12.8MHz
evanh:

--- Quote from: marmad on November 18, 2013, 02:22:34 pm ---
--- Quote from: evanh on November 18, 2013, 02:18:05 pm ---The maths is not the problem.  It's the stored trace that's the problem.  One method perform oversampling and filters only to the Nyquist point and stores those high-res samples as the trace.  The other method just stores 8-bit samples straight from the ADC ... which is nyquist limited and still only 8 bits.  Any further processing cuts-off even lower.

--- End quote ---
...
There is no such thing as oversampling when the DSO is already sampling at it's maximum rate. I can't speak about the DS1000Z, but the Rigol DS2000 series can sample at it's maximum 2GSa/s rate down to 2ms/div - it doesn't need to oversample because the sample memory already contains all possible samples that could be captured in a given time frame.
--- End quote ---
Except, of course, a DSO is often storing the trace at no where near it's ADC's max sample rate.  This is when oversampling kicks in.  An oversample situation is with respect to the stored trace, not the ADC.  When the trace is stored at, say, one sample per minute there is certainly some room for oversampling wouldn't you think?

There is a distinct acquisition mode change here, it changes the content of the stored samples.  The Rigol's don't attempt to perform this function and therefore are not implementing a high-res acquisition mode.
evanh:

--- Quote from: Galaxyrise on November 18, 2013, 04:34:40 pm ---
--- Quote from: evanh on November 18, 2013, 12:45:06 pm ---I bet Rigol's method could be, but it doesn't let you, flipped on and off - refreshing the display in either Normal or High Res without any new trace acquisitions.
--- End quote ---
I think this is a clue to Evan's issue.  As far as I know, the only time Rigol doesn't let you change the High Res setting on existing data is in record mode.  It absolutely does let you change the setting when stopped normally.
--- End quote ---
The setting is editable but it doesn't action until the next capture.  I was only giving an example of what could happen because the stored trace is no different between Normal mode and High Res mode.  Which is not the case on scopes that have a true high-res acquisition mode.

I can assure you this is a big issue for everyone.  Rigol's High Res mode should be avoided.  It will create problems if used.
marmad:

--- Quote from: evanh on November 19, 2013, 12:32:18 pm ---There is a distinct acquisition mode change here, it changes the content of the stored samples.  The Rigol's don't attempt to perform this function and therefore are not implementing a high-res acquisition mode.
--- End quote ---

Wrong. Acquisition modes change what is shown on the oscilloscope screen. There is sample memory and there is display memory. Whether a mode changes what is stored in the sample memory - or whether it performs the math between sample and display memory - is the prerogative of the DSO manufacturer. As I've mentioned half a dozen times already, there is NO MATHEMATICAL DIFFERENCE (except for speed) in performing successive sample averaging on samples as they arrive from the ADC @ 2GSa/s - or performing it on samples that have been saved in sample memory @ 2GSa/s.

I can clearly see the effects of the successive sample averaging filter on my Rigol DS2000 with simple sweep tests - as I've posted here. Whether it works correctly on your slower (and less capable) DS1000Z, I couldn't say - but it's certainly implemented on my DS2000.


--- Quote from: evanh on November 19, 2013, 12:46:35 pm ---I was only giving an example of what could happen because the stored trace is no different between Normal mode and High Res mode.  Which is not the case on scopes that have a true high-res acquisition mode.
--- End quote ---

Sorry, you're just spouting nonsense that's not backed up with any data (as usual). Successive sample averaging can be performed on a stored waveform at any time - it just requires a single waveform (whereas successive capture averaging, which requires multiple waveforms, can not). Of course, the speed at which that waveform was sampled will effect the LPF of the averaging - but other than that, it makes no difference.


--- Quote from: evanh on November 19, 2013, 12:46:35 pm ---I can assure you this is a big issue for everyone.  Rigol's High Res mode should be avoided.  It will create problems if used.
--- End quote ---

 ;D  Avoid it on your DSO if you want... I've already posted the stopband frequencies for the High Res averaging on the DS2000 from 5us-10ms here. Other users just need to be aware of them to use High Res problem-free.
evanh:
Display rendering is separate from acquisition.

High-res acquisition mode operates in oversampling only, not the stored trace.  The stored trace is the end result of acquisition.  All the filtered frequencies are beyond the Nyquist point.

Rigol doesn't do this, so, although it is high-res, it's not an acquisition mode.
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