Thank's for looking at HiRes modes of DS2000 vs DS1000Z series, this is actually pretty interesting and seldom being done or look during most "reviews".
You're welcome.
Your tests are even more interesting for me as after playing with my DS1104Z at HiRes mode I get feeling that is is acting bit "strange". But while I do not have experience with other scopes couldn’t tell if that is the problem with implementation of HiRes in DS1000Z or it is just the way HiRes is working.
No, there are definitely some strange things going on with the implementation on the DS1000Z. The DS2000 follows the mathematical model of successive sample averaging quite well, while the DS1000Z seems to be doing things poorly in comparison.
It's not clear exactly when/how well it works for each possible memory depth setting - the 12k and 120k setting seem to do some averaging in the us/div range, while the 1.2M and higher settings seem to do almost nothing unless in the ms/div and slower ranges (perhaps higher memory depths overwhelm the ability of the engine to keep up unless at slower sample rates). There also seems to be a problem with higher frequencies leaking past the stopband sometimes, as shown by the alias of the 10MHz sine in my previous images (and in the image of the sweep roll-off @ 12k below).
One thing I wanted to mention: I really think the name "High Resolution" is a bit of a misnomer. You won't all of a sudden get more pixels on your DSO display, or a more detailed vertical scale - the results of the averaging still have to be downsampled again for display memory. So it really should just be called "Sample Average" to avoid confusion (with normal Average renamed to "Waveform Average").
It's basically just a low pass filter with a sharp roll-off to a null, then subsequent peaks and nulls through the stopband (as shown in my previously posted image). To better illustrate this, I sent a repeated sine sweep pattern to my DS2000 in Normal mode:
When I turn on High Res (@ 1.4M), you see the sweep BW roll-off, just as you should:
When I switch the memory depth to 14k, the roll-off gets sharper because of the lower sample rate (thus lower bandwidth):
Here is the same signal to the MSO1000Z:
When I turn on High Res (@ 12M), there is very little change:
When I switch the memory depth to 120k, there is a roll-off, but fairly gentle:
When I switch the memory depth to 12k, there is a sharper roll-off, but then a rise again - almost like a notch filter:
Could You do bit more comparison of HiRes modes, including Noise Test but with lower frequency, so HiRes engine could actually show how it is handling noise signal, just practical case where HiRes should give different results from Averaging.
Average mode is good for removing non-repetitive noise - no bandwidth is lost, but the trade-off is some throughput (wfrm/s).
High Res mode is good for removing both repetitive and non-repetitive noise - no (or little) throughput is lost, but the trade-off is quite a bit of bandwidth (depending on desired bits of resolution).
Here's
a link for a good .PDF document describing the two types of averaging.
It's hard to get/make a perfect example to demonstrate, but here is a 500Hz sine wave w/repeating high frequency spikes, in Normal mode, Average mode, and then High Res - which recovers the original sine wave fairly well:
And here is a sine wave FFT - in Normal, then High Res/Deep memory (then High Res/Low memory on DS1000Z):
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