In described examples, embodiments include a circuit simulator having a processor and a memory. The memory stores at least one digital circuit element definition. The memory also stores at least one analog circuit element definition. The memory also stores at least one connect element definition, the connect element definition having at least one input coupled to the output of the digital circuit element definition and at least one output coupled to the analog circuit definition. The connect element definition includes at least a first current source coupled to the at least one output and a first impedance coupled to the at least one output, a signal on the at least one input determining the value of the first impedance.