Analog vs. digital simulation

Analog simulation and digital simulation differ in the following ways:

  • The goal of digital simulation is much simpler to achieve than analog simulation because the circuit is discrete in nature and has no circuit constraints to meet, such as Kirchhoff's Current Law (KCL).
  • Digital simulation runs orders of magnitude faster than analog simulation because digital simulation deals with high-level behavior only, while in analog simulation the same elements have analog implementations.
  • Digital simulation abstracts away important electrical characteristics that might be revealed by the analog simulation.

Mixed-mode simulation

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.

  • The logic levels on connected components do not match.
  • An analog probe is placed on the circuit.
  • The rise time or fall time of the digital component is not 0 in the configuration pane.