Learning Library · Oscilloscope specs, explained · 1
8-bit vs. 12-bit resolution
An oscilloscope's analog-to-digital converter (ADC) turns the voltage at each sample into one of a fixed number of levels. An 8-bit ADC has 256 of them. A 12-bit ADC has 4,096. Sixteen times as many levels means sixteen times finer steps on the same screen.
Top: the whole screen, with the zoom window marked. Bottom: the zoom window, magnified vertically. Yellow is 8-bit, blue is 12-bit, grey is the true signal.
Step size is set by the screen, not the signal
The ADC's range follows the vertical scale. With eight divisions on screen at 10 mV/div, the full scale is 80 mV. An 8-bit ADC splits that into 256 steps of about 313 µV. A 12-bit ADC splits it into 4,096 steps of about 19.5 µV. Some scopes digitize a range a little wider than the visible screen, so check the datasheet for the exact figure.
| Vertical scale | Full scale (8 div) | 8-bit step | 12-bit step |
|---|---|---|---|
| 1 mV/div | 8 mV | 31.3 µV | 1.95 µV |
| 10 mV/div | 80 mV | 313 µV | 19.5 µV |
| 100 mV/div | 800 mV | 3.13 mV | 195 µV |
| 1 V/div | 8 V | 31.3 mV | 1.95 mV |
Where 12 bits pays off
Extra resolution matters when you need to see something small on top of something large without changing the scale: ripple on a power rail, a small step in a large sensor output, the switching-node detail in a power converter, or the low-level tail of an audio or medical signal. With 8 bits you would have to zoom in on the scope's vertical scale and lose sight of the large signal, or rely on averaging, which only works on repetitive signals.
Try this
- At the default settings, look at the zoom window. The small detail spans only a few 8-bit steps, so the yellow trace is a coarse staircase. The blue trace follows its shape.
- Shrink the signal swing to a fraction of the screen. Now the 8-bit trace uses only a handful of levels in total. Using the full screen height is the first habit of good resolution.
- Turn the detail down to zero and back up slowly. Watch at what size each trace first shows it.
More bits do not guarantee more real resolution. The front-end noise has to be lower than the step size for the extra bits to carry information. That is what ENOB, the effective number of bits, measures.
UNI-T 12-bit oscilloscopes
UNI-T's HD oscilloscopes, including the UPO1000HD, MSO1000HD, UPO2000HD, MSO3000HD, MSO5000HD, and MSO8000HD series, use 12-bit vertical resolution. The X and E series use 8-bit converters.
See the detail without changing scale. 12-bit HD oscilloscopes from 70 MHz to 8 GHz.
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