IsSpice4 provides a quantum leap in performance over other analog and mixed mode simulators. It is the first commercially available version of SPICE based on Berkeley SPICE 3F.5 and XSPICE. (Detailed IsSpice4-Berkeley SPICE Differences)

IsSpice4 allows you to explore circuit performance by interactively running different analyses and sweeping any circuit variable. With the ability to simulate electrical, sampled-data, mechanical, physical, thermal, and other systems, IsSpice4 is the ONLY true interactive native mixed mode SPICE 3/XSPICE based simulator. The advanced features of IsSpice4 allow all types of applications to be simulated: switch mode power supplies, mixed signal ASICs, RF communication systems, interconnects, control systems, and mixed mechanical/physical systems.

Intusoft has spent hundreds of man-hours improving SPICE. And although IsSpice4 is based on SPICE 3, Intusoft has greatly enhanced the program over and above the public domain version and added more features, an interactive interface, superior analysis and model support, and improved convergence algorithms - all for a price no one can match. IsSpice4 is simply the best and most affordable SPICE program on the market today. Just take a look at some of its features:

State-of-the-Art Operation

  • Native mixed mode simulation - IsSpice4 includes an event driven simulator that supports mixed analog, digital and DSP circuits.
  • Interactive Operation - IsSpice4 operates interactively, and frees you from the restrictive batch style of older SPICE simulators.
  • Interactive Command Language - Comprehensive set of functions for batch style control of the simulator
  • NEW Automatic Stress Alarms - Set up automated alarms on any circuit quantity which will be triggered if the test doesn't meet specification
  • Visual Basic Scripting - Drive IsSpice4 using VB scripts from popular programs like Excel.
  • OLE/ActiveX Interface - Develop your own OLE/ActiveX interfaces

Built-in Models

  • Elements: Resistors, Capacitors, Inductors, Coupled Inductors, Transmission Lines, BJTs, JFETs, MOSFETs (Level 1-8), GaAs Mesfets, Switches, and Boolean logic expressions.
  • Behavioral Modeling: In-line Equations, Table models, If-Then-Else, Laplace expressions
  • Digital and AHDL Models: Digital primitives, State Machine, Frequency Divider, RAM, Sampled-Data Filters, Nonlinear VCOs, Laplace Equations

Advanced Models

  • HDL Modeling (XDL) for top-down design; Create models based on a powerful nonproprietary HDL using C.
  • Support for non-electrical applications and top-down system design.
  • Three types of digital/mixed mode modeling.
  • Lossy (distributed) transmission lines with frequency dependent losses.
  • MOS: BSIM1, BSIM2, BSIM3 version 2 & version 3.1 and FD SOI MOSFET models.
  • MESFET: Statz, Curtis-Enttenburg, Parker-Skellern, and HEMT models.


  • AC, DC, transient, noise, Fourier, distortion, transfer function, temperature, DC sensitivity, AC sensitivity and Pole-Zero analyses
  • Monte Carlo Analysis: Statistical yield analysis of circuit performance
  • RSS, EVA, Worst Case, and Sensitivity analyses using AC, Dc, Transient or operating point information
  • Randomly vary circuit parameters to test performance
  • Circuit Optimization: Automatically find a parameter value to maximize a user defined objective function
  • Temperature variations on individual elements
  • Parametric: automatic curve family generator
  • Failure Analysis
  • Design Validator feature for automatic design verification and automated measurements
  • Test Designer Fault Analysis and Software Test Set Design

Additional Interactive, AHDL & Mixed Mode Features

  • Real-time Display of voltages, currents and power dissipation
  • Simulation Scripts: a robust scripting language that allows simulation breakpoints and loops of different analyses to be run as a test procedure.
  • Interactively run analyses without having to edit the netlist or restart the simulator, add, delete, or rescale waveforms on the real-time display
  • Native Mixed Mode: IsSpice4 includes a 12 state digital simulator and models with timing information
  • Sweep parameters one at a time or in groups with great ease
  • Start, stop, pause, change, or resume any analysis on demand
  • Use C code subroutines & AHDL Models based on XSPICE

Convergence and Speed Improvements

  • Automatic Gmin stepping/Source stepping algorithms
  • New Pseudo-Transient algorithm
  • Improved Predictor-Corrector, Latency, and Bypass algorithms
  • Improved program defaults
  • Special Circuit Debugging Options
  • Full Gear Integration option


  • Works with ALL popular schematic entry programs
  • Accepts Berkeley SPICE 2G.6 or 3F.2 syntax; Outputs SPICE 2 and 3
  • True ActiveX Integration with popular schematic entry programs (e,g, Mentor Graphics' DXAnalog)