Question: I am running a Probe AC Analysis on my schematic. If I enable the Voltage option under the
Vertical menu, I can click on any of the nodes in the schematic, and the appropriate waveform will be
displayed. If I then enable the Onoise option under the Vertical menu and click in the schematic, nothing
will happen. My previous voltage waveforms stay on the screen, but no noise waveform is displayed.
Answer: In AC analysis, the network equations are structured differently when computing noise
waveforms, so it is not possible to simultaneously plot noise variables and other types of variables such
as voltage and current. You will need to delete the displayed voltage waveforms. Once this is done, the
noise waveform can be plotted.
Starting with Micro-Cap 8 version 8.0.9, when the Many Curves option is selected under the Probe menu, the
waveform types that are not available to be plotted with the displayed waveform will have their options
disabled in the Vertical menu. For example, if a voltage waveform is currently displayed, the Inoise and
Onoise options will be disabled. To access these options again, all of the displayed plots must be cleared.
Question: When I plot Onoise in a Probe AC Analysis, how do I know which node it is referring to?
Answer: The Onoise waveform will always refer to the Noise Output node specified in the AC analysis
limits dialog box. To access the limits dialog box in probe, go to the Probe menu and select Limits or just
hit the F9 hotkey. The Noise Output field should be specified with either the node name or the node number
of the desired output node. The Noise Input is also specified in this same dialog box and should be defined
with the Part attribute name of a source.
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