All major vendors offer high-resolution mode in their scopes. This is a mode that both increases bits of resolution as well as reduces noise. In high-res mode, the ADC oversamples and then applies a filter. A boxcar filter is typically used to average intermediate hypersamples. On many scopes, a user in high-res mode can specify bits of resolution and this choice determines the length of each boxcar filter. For example, if a scope with an 8 bit ADC is set to high-res mode and a value of 11 bits of resolution, each boxcar will consist of 8 (23) ADC sample points.
A boxcar DSP filter will average these samples and store the resulting average vertical value to the scope’s acquisition memory as the sample rate shown on the scope’s screen. This allows for statistical elimination of a good portion of internal scope noise as shown in figure 6. The most important attribute of high-res mode is its ability to reduce overall scope noise. High-res mode can reduce internal scope noise by up to a factor of 3. Tradeoffs associated with high-res mode are reduced bandwidth and a decrease in throughput. As the scope needs to perform additional processing with the DSP filters, update rate slows.
Real-time mode with high-res
Figure 5: If your scope has excess sample rate relative to needed bandwidth, turn on high-res mode to increase bits of resolution and reduce scope noise as shown. Using oversampling and digital filtering, and 8-bit scope can achieve 12 bits of resolution
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