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 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.
The table below gives detailed information on the usage of each SPICE source.
| Syntax | PULSE(V1 V2 TD TR TF PW PER) |
| Example | VIN 3 0 PULSE(-1 1 2NS 2NS 2NS 50NS 100NS) |
| Parameter | Description | Default | Units |
| 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 |
| 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 | Frequency | 1/Tstop | Hz |
| TD | Delay | 0.0 | Seconds |
| THETA | Damping Factor | 0.0 | 1/Seconds |
| 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 |
| 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 |
| 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 |