Products > Test Equipment

REVIEW - Rigol DS2072 - First Impressions of the DS2000 series from Rigol

<< < (342/566) > >>

evanh:
Rigol's method stores only 8 bit samples.  There is never any oversampling.  It's not an acquisition mode at all.  Any "high-res'ing" is derived, at display time, from what is stored.  It can only add low-pass filtering on top of what's stored, and what's more it doesn't even say how severe this filter is let alone have any parameters.

Agilent's high-res builds the stored trace.  Agilent's method has higher bit depths per sample point which uses oversampling when suitable.  It need not create any extra filtering beyond the stored sample rate ... and probably ensures it never does by adjusting the bit depth accordingly.

That's the difference and it's significant.

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.  Where as Agilent's method has no change in display because it's purely done at acquisition time.


Evan

marmad:

--- Quote from: evanh on November 18, 2013, 12:45:06 pm ---Rigol's method stores only 8 bit samples.  There is never any oversampling.  It's not an acquisition mode at all.  Any "high-res'ing" is derived, at display time, from what is stored.
--- End quote ---
Again, it makes NO DIFFERENCE whether you perform the math on already stored samples or samples as they're acquired. It's just math. I think you're hung up on believing 'acquisition mode' means that it has to happen between acquisition and sample memory - as opposed to acquisition and display.


--- Quote ---It can only add low-pass filtering on top of what's stored, and what's more it doesn't even say how severe this filter is let alone have any parameters.
--- End quote ---
As I mentioned in my previous post, I ran some tests on the Rigol to determine the LPF bandwidth of the successive sample averaging - and it's quite predictable.


--- Quote ---Agilent's method... need not create any extra filtering beyond the stored sample rate ... and probably ensures it never does by adjusting the bit depth accordingly.
--- End quote ---
It automatically creates filtering by virtue of doing successive sample averaging. This is a GIVEN of the technique. Says Agilent: "High Resolution mode limits the oscilloscope's real- time bandwidth because it effectively acts like a low-pass filter."

evanh:
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.

marmad:

--- 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 ---

So the Agilent X-Series is sampling faster than 2GSa/s @ 5us/div?

If the Agilent is NOT sampling faster than 2GSa/s @ 5us/div, please explain to me how the two following techniques are different:

The Agilent samples at 2GSa/s and averages every N samples into a single sample, down samples, and stores it for the display.
The Rigol samples at 2GSa/s and stores the samples. Later, it averages every N samples into a single sample, down samples, and moves it to the display.

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.

There's obviously no difference between averaging 256 samples in a row from an ADC running @ 2GSa/s - than from averaging 256 samples in a row from samples stored in memory @ 2GSa/s.

Galaxyrise:

--- 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.

There's a practical difference between the two approaches and it affects record mode: You get to store fewer waveforms if you want the high res averaging. This bothered me at first, too, but it's never actually mattered to me in practice.

Does Agilent's trigger ever use the high res data? That's another possible difference.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod