SPICE Source Types and Parameters

Overview

The NI SPICE Simulation Fundamentals series is your free resource on the internet for learning about circuit simulation. The series is a set of tutorials and information on SPICE simulation, OrCAD pSPICE compatibility, SPICE modeling, and other concepts in circuit simulation.

For more information, see the SPICE Simulation Fundamentals main page.

The series is divided among a number of in-depth detailed articles that will give you HOWTO information on the important concepts and details of SPICE simulation.

Circuit simulation is an important part of any design process. By simulating your circuits, you can detect errors early in the process, and avoid costly and time consuming prototype reworking. You can also easily swap components to evaluate designs with varying bills of materials (BOMs).

 

SPICE Simulation Sources

SPICE allows users to specify input that varies in form. These inputs are used as voltage or current signals that drive circuitry during simulation. In Multisim, these sources are available in the Sources group of the master database.

The following sources are available in SPICE simulation.

 

Using SPICE Simulation Sources

The table below gives detailed information on the usage of each SPICE source.

 Pulse

 

 Syntax PULSE(V1 V2 TD TR TF PW PER)
 Example

VIN 3 0 PULSE(-1 1 2NS 2NS 2NS 50NS 100NS)

 

 Parameter Description DefaultUnits
 V1 Initial value  Volts or Amps
 V2 Pulsed value  Volts or Amps
 TD Delay time 0.0 Seconds
 TR Rise time Tstep Seconds
 TF Fall time Tstep Seconds
 PW Pulse width Tstop Seconds
 PER Period Tstop Seconds

 Sinusoid

 

 Syntax SIN(VO VA FREQ TD THETA)
 Example

VIN 3 0 SIN(0 1 100MEG 1NS 1E10)IN 3 0 PULSE(-1 1 2NS 2NS 2NS 50NS 100NS)

 

 Parameter Description Default Units
 V0 Offset  Volts or Amps
 VA Amplitude  Volts or Amps
 FREQ Frequency1/Tstop Hz
 TD Delay 0.0 Seconds
 THETA Damping Factor 0.0 1/Seconds

 Exponential

 

 Syntax EXP(V1 V2 TD1 TAU1 TD2 TAU2)
 Example

VIN 3 0 EXP(-4 -1 2NS 30NS 60NS 40NS)

 

 Parameter Description Default Units
 V1 Initial value  Volts or Amps
 V2 Pulsed value  Volts or Amps
 TD1 Rise delay time 0.0 Seconds
 TAU1 Rise time constant Tstep Seconds
 TD2 Fall delay time TD1 + Tstep Seconds
 TAU2 Fall time Tstep Seconds

 Piece-Wise Linear

 

 Syntax PWL(T1 V1 <T2; V2 T3 V3 T4 V4 ...>)
 Example

VCLOCK 7 5 PWL(0 -7 10NS -7 11NS -3 17NS -3 18NS -7 50NS -7)

 

 Parameter Description Default Units
 V1 Instantaneous voltage  Volts or Amps
 T1 Instantaneous time  Seconds

 Single Frequency FM

 

 Syntax SFFM(VO VA FC MDI FS)
 Example

V1 12 0 SFFM(0 1M 20K 5 1K)IN 3 0

 

 Parameter Description Default Units
 V0 Offset  Volts or Amps
 VA Amplitude  Volts or Amps
 FC Carier frequency 1/Tstop Hz
 MDI Modulation index  Seconds
 FS Signal frequency 1/Tstop Hz

 

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