ICAP/4 is Intusoft's fourth generation analog and mixed signal circuit simulation package (ICAP/4 brochure in pdf format, 293k). The basic package consists of:

  • IsSpice4, a Berkeley SPICE 3F.5 compatible simulation engine combined with the Georgia Tech XSPICE event driven simulator. (Feature set, Details)
  • SpiceNet, a revolutionary new schematic entry program that manages multiple circuit configurations and controls the simulator.
  • IntuScope, a heavy duty programmable waveform viewer.
  • Model Libraries. The EDA industry's largest and most extensive library. Over 23,300 models are available in a series of libraries that varies by product.

These core programs and more are integrated into a seamless package using Microsoft's ActiveX (formerly OLE) technology. Learn What's Makes Intusoft Different?

ICAP/4 is sold in a family of software packages with varying capabilities that were built to provide features you need at the right price. Click on the "Products" keyword at the top of this page to read about the many scalable ICAP/4 simulation offerings from Intusoft, and other offerings such as Magnetics Designer, CMSDK, and Test Designer.


Pioneering PC based workstation simulation, Intusoft introduced its original IsSpice simulator in 1985. Now, several generations of simulation technology later, the 4th generation IsSpice4 simulator combines Berkeley SPICE 3 (Simulation Program with Integrated Circuit Emphasis) analog simulation with the Georgia Tech XSPICE event simulator for a native mixed-signal simulation capability. Added to both of these technologies is an interactive capability that lets you make parameter modifications and watch the simulation results instantly. (Detailed IsSpice4-Berkeley SPICE Differences)

The IsSpice4 simulator uses the Microsoft ActiveX technology to provide an automation interface so that the simulator can be controlled using external scripts as well as the internal scripts implemented in Berkeley SPICE3. Intusoft is the only commercial SPICE vendor that implements and extends the Berkeley script language introduced with SPICE3. This important feature allows IsSpice4 to make and record sophisticated measurements of circuit performance; for example, rise time, gain margin or propagation delay. These automatic measurements are set up and made available to the user through the SpiceNet schematic package.

The IsSpice4 specification describes the analysis types and built in models that IsSpice uses. A feature summary is also available.

How it works:

The simulator itself works by formulating the KCL, Kirchoff current law equations, summing the currents at each node and setting the result equal to a constant. This admittance matrix is modified in SPICE3 to hold the Independent voltage sources and in XSPICE to contain state variables. The matrix itself is referred to as a Modified Nodal Admittance, MNA, matrix.

For DC and operating point analysis, the MNA matrix solution is iterated, and the new MNA values are re-computed at each iteration until a stable result is achieved. Certain circuits like flip-flops can cause the simulator to oscillate between stable solutions. When this happens, the simulator uses certain heuristic tricks to stabilize itself (Gmin stepping, source stepping, …).

An important property of electronic circuits is that connectivity is generally between neighboring parts. If the MNA matrix is ordered along the signal flow, entries tend to fall near the main diagonal with most matrix entries being zero. This is called a sparse matrix and its solution, performed using L-U factoring, is done using an efficient set of procedures that maximizes the sparseness of the matrix by reordering and then using a system of pointers to minimize memory utilization. This makes it possible to solve large systems of equations, i.e. 50000 x 50000, within the RAM limitations of modern workstations.

For transient solutions, it is necessary to linearize the circuit about its non-linear operating point at each time point. Then the dynamic circuit change with time is accounted for by iterating the solution until the error estimate at the next time is less than a pre-established amount. IsSpice4 uses several tricks to reduce the computational load including forward predicting the states and node voltages for the next time step and by bypassing the matrix load operation for parts that have little or no change in their inputs. Many other simulators do not have this feature.

For AC analysis, the problem is considerably simpler. Once the operating point is established, a small signal equivalent circuit is made and a single matrix solution is performed for each frequency. Since no iterations are required, the solution is exact, other than for errors created by the finite computer word length. AC analysis is therefore more precise and faster than transient analysis.

The XSPICE event simulator actually has 2 benefits. The first is to extend the number of primitive models that SPICE can have beyond it original 26 model limit. In accomplishing that, much of the bookkeeping needed to add a SPICE model was swept away, to become the responsibility of procedures added by the Georgia Institute of Technology. Then Georgia Tech added a method of abstracting model properties into a tabular definition that is compiled into C code using their code model software. For models that required event driven simulation, they added the event scheduling software and the whole thing was hooked into the SPICE3 code, mainly in the DCTRAN procedure. Intusoft added a Dynamic Linked Library, DLL, interface so that it is no longer required to recompile the entire SPICE program when a code model is added. You can just drop the DLL into the IsSpice folder and IsSpice will hook the models to itself. The result makes IsSpice perform digital simulation along with analog and provide a really easy method for users and Intusoft to add and manage new IsSpice4 models. An incredible amount of grunt work was eliminated from making an IsSpice primitive model, allowing the user to concentrate mainly on coding model equations. This capability is sold separately in the CMSDK product. Intusoft was the FIRST vendor to incorporate XSPICE technology into its SPICE tools.

 IsSpice4 Specifications

Analysis Types
AC Frequency response, Bode Plot, Small Signal Linear analysis
DC DC source sweep
TRAN Nonlinear Transient analysis
OP Operating Point
DISTO Small Signal Distortion analysis
NOISE Small Signal Noise (shot, flicker, thermal) analysis
FOURIER Time to Frequency transformation
POLE-ZERO Pole-Zero analysis
DC Transfer Function Input-Output Impedance and gain
TEMPERATURE Circuit and Part Temperature sweeps
SENSITIVITY Works for AC, DC, Transient and OP analyses using Perturbation analysis
Design Validation Automatic User-defined Measurements matched against test limits, includes summary report
Stress Alarms Automatic user defined Alarms monitor any circuit quantity, includes summary report of failed tests
PARAMETRIC Parameter sweeping analysis with the Curve Family wizard (Interactive, batch or script style)
MONTE Monte Carlo statistical yield analysis
OPTIMIZATION Single parameter, single nonlinear function optimization
RSS Root Sum Square
EVA Extreme Value Analysis
Worst Case Worst Case Analysis with sensitivity sign change warning
ICL, Interactive Command Language Combination of any/all of the above using a scripting language, accessible from Visual Basic or ActiveX

Built-in Transient Signal Generators (many other generators are available in the ICAP/4 models libraries (NTSC, 3 Phase, Sawtooth, FSK, PSK, Random Noise, Repeating PWL with data from a file, etc.)

  • PULSE Pulse
  • SIN Sine or damped sine wave
  • PWL Piece wise Linear
  • SFFM Single Frequency FM
  • EXP Exponential pulse

Integration Methods

  • Trapezoidal
  • Gear

IsSpice Models (Built-in)

  • A, reserved for code models, see below
  • B Behavioral, current or voltage source controlled by an algebraic expression, plus the following Intusoft extensions:If-Then-Else, borrowing from C shorthand <expression> ? <return this is true> : <else return this if false> for example; …v=v(1) > .5 ? 1 : 0 is a simple limiter Boolean expressions, use & for logical AND | for logical OR and ! for logical NOT; for example… v=V(1) & V(2) | !V(4)
  • C Capacitor, extended to use B element type expressions
  • D Diode, PN junction diode
  • E Voltage controlled voltage source
  • F Current controlled current source
  • G Voltage controlled current source
  • H Current controlled voltage source
  • I Independent current source
  • J JFET, several model levels (Hemt)
  • K Mutual Inductance
  • L Inductance
  • M MOSFET, (SPICE Levels1-8, BSIM1, BSIM2, BSIM3 v2 and v3.1, BSIM4)
  • N no model assigned
  • O Lossy (RLCG) distributed transmission line with skin effect and dielectric loss
  • P no model assigned
  • Q BJT (Gummel-Poon)
  • R Resistor, extended to use B element type expressions
  • S switch, voltage controlled
  • T lossless transmission line
  • U RC transmission line
  • V Independent voltage source
  • W Switch, current controlled
  • X Subcircuit
  • Y no model assigned
  • Z Mesfets - Statz, Curtis-Ettenburg, Parker-Skellern
  • Analog Behavioral Modeling

  • Arbitrary mathematical equations
  • Nonlinear Differential equations
  • Complete set of math operators (trigonometric, transcendental, algebraic)
  • Time and Frequency domain including Z domain and Laplace equations
  • Boolean Logic Expressions
  • If-Then-Else Expressions
  • Analog C Code (AHDL) Models

  • Core, Magnetic Core
  • Convolution Filter
  • D_dt, Time-derivative
  • Fdsoin, N Channel fully-depleted SOI MOSFET
  • Fdsoip, P Channel fully-depleted SOI MOSFET
  • Hyst, Hysteresis
  • Lcouple, Inductive coupling
  • Limit, Limiter
  • Oneshot, Controlled oneshot
  • PWL, Piece-wise linear waveform stimulus, repeating, data from a file
  • S_xfer, s-domain (Laplace) transfer function
  • Slew, Slew rate follower
  • Sine, Controlled sine wave oscillator
  • Square, Controlled square wave oscillator
  • Table-based transfer function with and without end point limiting
  • Triangle, Controlled triangle wave oscillator
  • Vswitch, Smooth transition switch
  • Hybrid C Code (AHDL) Models

    • Digital-to-Analog Node Bridge
    • Analog-to-Digital Node Bridge
    • Digital-to-Real Node Bridge
    • Real-to-Analog Node Bridge
    • Analog-to-Real Node Bridge
    • Voltage Controlled Digital Oscillator

    Real (Sample-Data System) C Code (AHDL) Models

    •  Z-Transform delay
    • Gain Block

    Digital C Code (AHDL) Models

    • Buffer
    • Inverter
    • And
    • Nand
    • Or
    • Nor
    • Xor
    • Xnor
    • Tristate
    • Pullup
    • Pulldown
    • Open Collector
    • Open Emitter
    • D Flip Flop
    • JK Flip Flop
    • Toggle Flip Flop
    • Set-Reset Flip Flop
    • D Latch
    • Set-Reset Latch
    • State Machine
    • Frequency Divider
    • RAM
    • Digital Source
    • MIDI Digitally Controlled Oscillator

     Salt Models (with model source code)

  • Source (repeating PWL source, X, Y data from file)
  • Source (true random noise source)
  • Convolution filter
  • Array processing block
  • OLE/ActiveX server template
  • PC hardware device interface (microphone, speaker)
  • Analog Output Board interface
  • Data Acquisition Card interface
  • Did You Know Intusoft Was the First?

    The following is a list of capabilities that Intusoft introduced to the analog simulation world.

    SPICE 2 Models for: IGBTs, fuses, lasers, vacuum tubes, generic template models, dual gate Mosfets, SC filters, neural networks, digital gates, RF beads, IBIS buffers, saturable cores, and PWMs (using the state space approach)

    Products/Features: 32-bit version of SPICE for DOS, 64-bit version of SPICE for windows, integrated schematic entry including patented layering capability, SPICE 2 compatible model generation software (now SPICE3.F5), parameter passing, analog and mixed-signal fault and test diagnosis, automated setting/recording of electrical measurements across designs with stress alarms, schematic-less device sweeping, magnetics design and synthesis, DSP simulation and firmware.