Circuit Simulation Using SPICE

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Circuit simulation using SPICE

Neuromorphic Engineering II

Institute of Neuroinformatics

University | ETH Zurich

Spring Semester 2008



Outline

What is SPICE?

How does SPICE work?

Tanner Tools TSPICE

S-Edit



SPICE Origins

SPICE is a computer program designed to simulate analog electronic

circuits.

It original intent was for the development of integrated circuits , from

which it derived its name: Simulation Program with Integrated Circuit

Emphasis.

1967 Prof. Ronald Rohrer of U.C. Berkeley develop ComputerAnalysis of Nonlinear Circuits, Excluding Radiation

(CANCER)

1972 CANCER was re-written and re-named to SPICE

(Version 1) and released to the public domain.

1975 Version 2 of SPICE was released (Version 2g6)

1985 Version 3 of SPICE was rewritten in C (rather than

FORTRAN) and released to the public domain.



SPICE Avaliable Packages

The SPICE home page:

http://bwrc.eecs.berkeley.edu/Classes/IcBook/SPICE/

Public Domain

Original Berkeley SPICE3f4 code:

ftp://ic.eecs.berkeley.edu/pub/Spice3/

NGSpice

http://sourceforge.net/projects/ngspice

Commercial

HSPICE (Synopsis)

PSCPICE (OrCAD)

SYMETRIX

TSpice (Tanner Tools)











SPICE Programming

SPICE is an interpreted language: In order for a computer to

understand the SPICE instructions you type, it must have the SPICEprogram (interpreter) installed. SPICE source files are commonly

referred to as netlists (or "decks") with each line in the file being called

a "card."

Writing a SPICE deck is like writing a good program

Plan: sketch schematic on paper or in editor.

Modify existing decks whenever possible.

Code: strive for clarity.

Start with name, email, date, purpose.

Generously comment.Test: Predict what results should be.

Compare with actual.

Garbage In, Garbage Out!



Solving differential equations

SPICE uses numerical techniques to solve nodal analysis of circuit.

The nature of SPICE’s iterative process allows it to simulate many

types of systems that can be modelled through standard equations

and differential equations.

Hodgkin and Huxley model of a neuron’s spike generating

mechanism.

Chaotic and Dynamical Systems

Diffusion equations



Spice components and analysis types

You can use SPICE to specify these circuit components: Resistors, Capacitors, Inductors

Independent sources (V, I), Dependent sources (V, I)

Transmission lines

Active devices (diodes, BJTs, JFETS, MOSFETS)

You can use SPICE to perform the following types circuit analysis:

Non-linear d.c.

Non-linear transient

Linear a.c.

Noise and temperature



SPICE common elemenets

Letter Element

R ResistorC Capacitor

L Inductor

V Independent Voltage Source

I Independent Current Source

M MOSFET

D Diode

Q Bipolar transistor

X Subcircuitr

E Voltage controlled Voltage SourceG Voltage controlled Current Source

H Current controlled Voltage Source

F Current controlled Current Source



Active components: the MOSFET device models

All Mosfet devices in SPICE reference a model by its instance name.

Each Mosfet model in SPICE has a keyword NMOS or PMOS , as well

as a Level parameter.

MOSFET TRANSISTOR MODELS:General form: .model [modelname] [nmos or pmos] [parmtr1=x] . . .

.model mod1 pmos

.model mod2 nmos level=2 phi=0.65 rd=1.5



MOSFET device model levels

Levels 1,2,3 (Berkeley SPICE 2g6): basic transistor equations.

Not very accurate, but fast.

Level 4 (BSIM1): accurate, based on the Berkeley short-channel

IGFET model.

Level 5 (Tanner, Maher-Mead): accurate physically based model,

continuous over all regions of operation, including subthreshold.

Levels 13, 28, 39, and 47: Based on Berkeley IGFET models

(BSIM, BSIM2, and BSIM3 models).

Levels 49 and 53 (BSIM3 Revision 3): most accurate models.Supported by most foundries and SPICE simulation engines.



SPICE Analysis Types

DC Operating Point Analysis .op: Computes circuit’s DC operating

point values.

DC Transfer Analysis .dc: Sweeps signals and computes operating

point values for all range of swept signals.

Transient Analysis .tran: Provides information on how circuit elements

vary with time.

Transient Powerup Analysis .tran/powerup: Sets the entire circuit to

zero for t = 0s. As the simulation proceeds, the voltage

sources are allowed to ramp up to their specified values.

Useful to define the initial state of a circuit which has no

definite DC steady-state condition.

AC Analysis .ac: Characterizes the circuits behavior dependence on

small-signal input frequency.



Why Tanner-Tools TSPICE

Integrated with L-Edit and S-Edit

Affordable (<2K, low maintenance fees)

Optimized for subthreshold circuits simulations

Table-based mode





TSPICE netlist example

Vdd

in Vout

Simulation commands (inverter_c.sp)

.options scale=0.8u deftables=0

.options maxmsg=1 modelmode=direct

.options abstol=1e-17 reltol=1e-7 chargetol=1e-19

.options absdv=0.01 accurate=1

.options js=1e-5

.include "inverter.sp"

vdd Vdd gnd 5

vin in gnd pwl( 0 0 5u 5 10u 0)

.tran/powerup 1u 10u

.print tran in out

options

circuitelements

commands



How does (T)SPICE work?

Not very well! Don’t ever believe it completely models reality.

Problems:

Very computer intensive.

Doesn’t model transistor mismatch. Doesn’t model Early effects well.

Doesn’t model distributed characteristics like resistance and

capacitance.

Makes you lazy about thinking.



T-SPICE and S-Edit



T-SPICE and S-Edit



T-SPICE and S-Edit

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Circuit Simulation Using SPICE