SPICE Simulation - The most common analog simulator, (Simulation Program with Integrated Circuit Emphasis)

   
 

From Xmultiple Engineering Dept.


Circuit simulators Are Available In Several Types.

Circuit simulators can be broadly grouped into those that simulate a circuit in an analog way, a digital way, or a combination of analog and digital.

This last category are often called mixed mode simulators since analog simulation is used for part of the circuit and digital simulation for the rest. The most common analog simulator, SPICE (Simulation Program with Integrated Circuit Emphasis), grew out of a class project and subsequent doctoral dissertation at Berkeley. It continues to be developed there and elsewhere. It is available as freeware (at least in demo versions) and as a commercial product from several companies. In this class Eldo, a commercial spice like simulator, will be used via direct invocation and via the DAIC user interface.
SPICE simulates a circuit by solving simultaneous differential equations that describe voltages or currents in a circuit network. The equations come from mathematical models for components such as resistors, capacitors, bi-polar transistors (BJT), MOSFET transistors, transmission lines, etc. While precision limited numbers are used in these calculations, numerical resolution is adequate to typically consider the nodal solutions to be continuous (watch out though, I have experienced circuits whose simulation showed behavior, caused by numerical limitations, not observed in a real circuit). For a SPICE simulation, the following are needed:

  • A mathematical model for each type of component in the circuit. For example a BJT.
  • Parameters for the component models that tailor the model to emulate a specific component. For example, a 2n2222 NPN BJT. For IC creation, MOS transistors are constructed using a specific companies fabrication process and thus the parameters from a specific fabrication process are needed.
  • A description of how components are connected to form the circuit. This is called a Netlist. A Netlist contains a list of components, interconnections, and various commands to the simulator.

 

Mentor and ELDO Analog Simulators

There are two user views of analog simulation with our mentor tools. The first is starting simulation from Design Architect - IC (DA-IC). The second is direct invocation of the simulator. When started from within DA-IC there are two parts to the analog simulation environment: the simulation kernel (or engine), which is Eldo, and the user interface within DA-IC. Eldo uses the same netlist format and has many of the same options as SPICE. The user interface creates a netlist file and a control file and starts the simulation engine (Eldo) which writes output files to disc. After simulation is finished, DA-IC launches Ezwave to view results as specified by the user. DA-IC is customized for IC design and thus when drawing schematics you wonˇ¦t find libraries of "off the shelf" logic or transistor components and the palette has been tuned for actions needed in IC design. It has a simulator user interface for creating and editing the netlist and control files file sent to Eldo.


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