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Analog vs digital X-Y mode
Fungus:
--- Quote from: tautech on March 22, 2018, 07:25:20 am ---We'll all know when DSO's have really come of age when they can handle Jerobeam Fenderson's oscilloscope music.
https://www.youtube.com/user/jerobeamfenderson1
Yummy stuff. :)
--- End quote ---
My cat loved it. :)
Tom45:
--- Quote from: rf-loop on March 22, 2018, 10:14:35 am ---Also with digital scopes there is one thing what also may affect result. There is some different methods to do X-Y
Some DSO's may use direcft XY plot method (read X and Y ADC and plot point and repeat)
--- End quote ---
Or instead of plotting points, draw a vector from Xn-1, Yn-1 to Xn, Yn
There is still the question of what sample rate to use. But I don't see any downside to oversampling. So why not sample as fast as possible.
But after thinking about it, perhaps the tricky part is how to emulate phosphor persistence.
David Hess:
--- Quote from: Tom45 on March 22, 2018, 04:03:32 am ---So why do digital scopes do so poorly in X-Y mode?
--- End quote ---
DSOs have six problems with X-Y mode:
1. Non-index graded displays cannot be anti-aliased and most DSOs with index graded displays do not anti-alias anyway or anti-alias poorly; this becomes an additional source of quantization noise. Note that the analog examples above show a raster displayed on a vector display device producing further aliasing on the DSOs. A true vector implementation would look better on both types of oscilloscopes.
2. DSOs suffer from quantization noise from the digitizer which is usually handled poorly in X-Y mode. High resolution mode should solve this. Average acquisition mode should also solve this unless it lowers the update rate.
3. Most DSOs produce display updates by batching record length groups of samples. If the vector generation time does not fill the record length evenly, then the display updates either miss or overlap sections. "Phosphor" type DSOs still update the display in batches determined by the number of samples between display updates.
4. DSO display refresh and update rate is orders of magnitude slower than the continuous update rate of an analog oscilloscope. This should not matter above about 60 Hz but combined with 3 above it becomes a problem.
5. Almost all DSO displays have a much lower resolution per area than an analog CRT. Many old CRT DSOs operated at 254dpi (100dpc) and could produce a pretty good vector display in X-Y mode except for the record length and update rate issues described above despite lacking anti-aliasing.
6. Most DSOs do not support a Z-axis (intensity) input so all of the vectors run together. The Rigol example above shows this.
These issues with DSO XY mode could be fixed to produce a display limited only by the display device itself but it is hardly a high priority.
T3sl4co1l:
Hey, I'm impressed those did as well as they did. :)
X-Y is a notoriously hard problem, and low on the list of priorities to address.
Tim
james_s:
I use XY when working on vector arcade boards, a scope is more convenient than having one of the (hard to find) 19" vector monitors and a power supply producing the multiple oddball voltages they require on the bench. At least I did before I built a 5" vector monitor for one of my other projects.
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