Integrated Circuit Simulation

Document Sample
Integrated Circuit Simulation Powered By Docstoc
					Integrated Circuit Simulation
Typical Integrated Circuit (IC) Design Flow
                    Integrated Circuit Simulation

• The Problem
  • Integrated circuits, unlike board-level designs composed of discrete
    parts, are impossible to breadboard before manufacture
  • the high costs of photolithographic masks and other manufacturing
    prerequisites make it essential to be able to efficiently
     • design the circuit to be as close to perfect as possible before the
         integrated circuit is first built. Simulating the circuit with SPICE
         is the industry-standard way to verify circuit operation at the
         transistor level before committing to manufacturing an integrated
     • Board-level circuit designs can often be breadboarded for testing.
         Even with a breadboard, some circuit properties may not be
         accurate compared to the final printed wiring board, such as
         parasitic resistances and capacitances.
                        Integrated Circuit Simulation

• The Solution
   •   Circuit performance can often be estimated more accurately using SPICE
       simulation. Also, designers may want more information about the circuit than
       is available from a single mock-up.
              • circuit performance is affected by component manufacturing
                  tolerances. In these cases it is common to use SPICE to perform
                  Monte Carlo simulations of the effect of component variations on
                  performance, a task which is impractical using calculations by hand
                  for a circuit of any appreciable complexity.
   •   Circuit simulation programs, of which SPICE and derivatives are the most
       prominent, take a text netlist describing the circuit elements transistors,
       resistors, capacitors, inductors, etc.) and their connections, and translate this
       description into equations to be solved. The general equations produced are
       nonlinear differential algebraic equations which are solved using implicit
       integration methods, Newton's method and sparse matrix techniques.

   Good thing we have powerful computers
                            Integrated Circuit Simulation

• Circuit Simulator Software
   •   The SPICE program (our Multisim software uses the SPICE engine as its basis), originated and
       developed at University of California at Berkeley, is truly a wonderful present to the electrical
       engineering community
   •   It allows us to simulate both individual devices and electronic circuits, performing a large number of
       different analyses needed for tasks such as verification of circuit designs and prediction of circuit
       performance. It is so flexible and usually so reliable that many engineers use it as a "software
   •   However, the results of a SPICE simulation are only as good as the device models and the device
       parameters used in the simulation. Device technologies change so fast and device characteristics are
       so different that just using default parameters is almost never justified. If wrong device parameters
       or models are used in a SPICE simulation, all this computer power will be wasted—true to the old
       adage: "Garbage in, garbage out".
   •   Less than a decade ago, a typical circuit simulator would run only on mainframe computers.
       However, the rapid progress in microcomputers has enabled the development of SPICE versions that
       can run on inexpensive machines, making advanced circuit simulators readily available practically
       to every electrical engineer and electrical engineering student (that’s you)
         •    Hence, we are now in the privileged situation that we can teach a course on the basics of
              semiconductor device physics and device modeling using the same computer aided design
              (CAD) tool that electrical engineering students will almost certainly use as practicing
              engineers. This fortunate circumstance allows students to try actual circuit design, bringing
              semiconductor device physics and modeling (which are often taught as a fairly theoretical
              subject) down to a very practical level.
                          Integrated Circuit Simulation

• Circuit Simulator Software
-Simulation Program with Integrated Circuit Emphasis, or SPICE, has been used for over
thirty years.

-The original implementation of SPICE was developed at the University of California
Berkeley campus in the late 1960s. SPICE was developed largely as a derivative of
CANCER (Computer Analysis of Nonlinear Circuits, Excluding Radiation) also developed
by UC Berkeley.

-The first widely used version of SPICE was announced in Waterloo, Canada in 1973.
Shortly thereafter SPICE was adopted by nearly all major engineering institutions
throughout North America. SPICE has evolved into the academic and industry standard for
analog and mixed-mode circuit simulation.

-Over the years additional simulation algorithms, component models, bug fixes, and
capabilities were added to the program. Even today SPICE is still the most widely used
circuit simulator in the world and as of 2006 the latest version is SPICE 3F5.
XSPICE was developed at Georgia Tech as an extension to the SPICE language. XSPICE
allows behavioral modeling of components which can drastically improve the speeds of
mixed-mode and digital simulations. Multisimm from National Instruments is based on
SPICE 3F5 and XSPICE and provides additional convergence and speed improvements to
complement these powerful simulation languages.