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| Dithering on 8-bit scope? |
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| Circlotron:
On a DSO that uses an 8-bit A/D converter, would it be possible to have an option where at slower scan rates you could have the LSB of the A/D dithered so as to gain several extra bits of resolution? And by dithered, I mean add a high frequency triangular signal of exactly 1 LSB peak to peak to the incoming waveform and then measure the duty cycle of the resulting LSB as it jiggles between two adjacent values to see where it lies between those two LSB values. Obviously this approach wouldn’t work at higher signal frequencies and scan rates because the A/D would be too busy, but at the lower end, particularly at audio frequencies it might have half a chance. So, would it be a practical thing to do? Or do some scopes already do this? |
| Fungus:
I don't know a 'scope that does it and they're not programmable. OTOH many 'scopes have a "high res" mode which averages adjacent samples. You can usually set the window size. There's also an "averaging" mode which overlays adjacent waves on top of each other when a signal is repetitive. Both these techniques can give a couple more "bits". |
| Circlotron:
My scope has both hi res and averaging modes. Naturally there is a limit to the resolution of the signal displayed on the screen because of the pixel pitch, but if the individual samples are logged and brought out externally to be examined, in hi res or average mode have they been truncated to 8 bits or do they have greater resolution? |
| tautech:
--- Quote from: Circlotron on August 20, 2023, 12:59:00 am ---My scope has both hi res and averaging modes. Naturally there is a limit to the resolution of the signal displayed on the screen because of the pixel pitch, but if the individual samples are logged and brought out externally to be examined, in hi res or average mode have they been truncated to 8 bits or do they have greater resolution? --- End quote --- Not only as oversampling is employed therefore limiting BW before the risk of aliasing. Also note how mem depth is automatically managed. Some examples from the 8 bit SDS1104X-E and can do more from other models if/as required. |
| tautech:
--- Quote from: Circlotron on August 19, 2023, 10:27:13 pm ---On a DSO that uses an 8-bit A/D converter, would it be possible to have an option where at slower scan rates you could have the LSB of the A/D dithered so as to gain several extra bits of resolution? And by dithered, I mean add a high frequency triangular signal of exactly 1 LSB peak to peak to the incoming waveform and then measure the duty cycle of the resulting LSB as it jiggles between two adjacent values to see where it lies between those two LSB values. --- End quote --- There are also other ways to accomplish this with vertical zoom however that is sometimes governed by channel offset limits and requires some mucking about to maintain that part of the waveform you need inspect more closely. But some modern scopes have an improved vertical zoom feature to keep the waveform part you need inspect on the display where in the following screenshots a 100x zoom has been applied from the 1V/div to 10mV/div which with a 10x probe = 1mV/div. With these there was a need to keep the trigger level setting on or near the display. |
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