Scaling a waveform for full-scale usage of the scope’s full 8-bit ADC is a step in the right direction. Why not increase the vertical zoom even more? If too much of the signal is above the top or below the bottom of the scope’s on-screen vertical limits, the scope’s ADC will be driven into saturation. When in saturation, the ADC will not produce valid results. The scope requires an unspecified amount of time to recover from saturation and during this recovery time, no measurements are valid.
Scope vendors specify an off screen dynamic range. This value is typically given in number of divisions that a signal can be driven off the top or bottom of the display without causing the ADC to be driven into saturation. This technique allows users some additional vertical zooms in order to apply more of the scopes vertical resolution to the portion of the signal on the display. Figure 3 shows an example where the user was about to double the vertical resolution by moving the signal to 4 divisions off screen, then adjust the vertical setting to achieve a 2X increase in resolution.
Figure 3: In this example with an Infiniium DSO9104A which has a +/- 8 division dynamic range setting, the user moved the signals 4 divisions off center in order to double the resolution they got when the entire waveform was displayed on screen Click on image to enlarge