Mixed-mode simulation refers to the simulation of circuits in which analog simulation and digital simulation coexist. Fundamentally, this type of simulation is possible because of the hybrid elements called bridges. A digital-to-analog (D/A) bridge translates digital signals into analog voltage levels. An analog-to-digital (A/D) bridge translates analog voltage levels into digital states. In addition to connecting elements in the circuit, the bridges play a key role in synchronizing the analog and digital simulators by signaling when new analog time steps and digital events are set.
D/A conversion of digital components
For circuits using the digital components, D/A bridges are added to convert digital simulation to analog simulation in the following scenarios. This conversion is indicated in the color change of the trace from blue to red.