Ngspice is a mixed-level/mixed-signal circuit simulator based on three open source software packages: Spice3f5, Cider1b1, and Xspice. Spice3 is the most famous and widely used circuit simulator. Cider is mixed-level simulator that includes Spice3f5 and adds DSIM, a device simulator. Cider couples the circuit level simulator to the device simulator to provide greater simulation accuracy (at the expense of greater simulation time). Xspice is an extension to Spice3 that provides code modeling support and simulation of digital components through an embedded event driven algorithm.
