Spice

Enrico Santi

Types of Analysis

• Bias point (always performed)

• .TRAN transient analysis

• .AC AC analysis (on linearized system)

• .FOUR Fourier analysis

• .DC DC sweep analysis

File Types

Input

• .CIR text file with circuit description

Output

• .OUT Spice text output (contains error messages and bias point info)

• .DAT Data file (used by Probe to plot)

Format of .CIR Files

Title

Circuit description

Analysis description

Output description (.PROBE)

End-of-file statement (.END)

Part Library

• Part library contains collection of subcircuits representing OPAMPS, IC chips, etc.

• Parts can be used to build circuits (node mapping)

Part Library and Subcircuit Syntax

.LIB eval.lib * include library eval.lib

Xname [nodes] SUBNAME * call statement

File eval.lib contains subcircuits:

.SUBCKT SUBNAME [nodes] circuit description.ENDS SUBNAME

Defining Model Parameters: the .MODEL statement

• Used to define model parameters

• Syntax for an NPN transistor with forward beta of 300Q1 1 2 3 QNAME.MODEL QNAME NPN (BF = 300) 1

3

2

Examples

• RC circuit (time domain and frequency domain)

• Astable circuit using 555 (use of library and subcircuits)

• Transistor current source (use of .MODEL statement to define component parameters)

Example: Highpass Filter

VG

C1

R1

+

-

+-

0

21

159K

10nF

RC highpass filter

VG 1 0 DC 10V AC 1

R1 2 0 159KC1 1 2 10NF IC=-5V

.TRAN 6us 6MS

.AC DEC 100 1HZ 10KHZ

.PROBE

.END

555 Astable