Unfortunately, there is no way to generate an analog graph from digital data in the software. The only way to visualize this information is to export the digital data, either the raw data using the main export feature, found here: Saving, Loading, and Exporting Data, or using the protocol export feature, found here: Using Protocol Analyzers.
It's definitely a good idea, and we've been thinking about it for a while. Ultimately we would like to add math channel features, as well as add support for protocol analyzers to produce analog graphs. However we haven't put this on the road map yet.
trello ID: 55fae18c0c78301027d36f49