

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?
IsSpice4
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 mixedsignal 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 IsSpice4Berkeley 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 recomputed at each iteration until a stable result is achieved. Certain circuits like flipflops 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 LU 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 nonlinear 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 preestablished 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 TypesAC 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 POLEZERO PoleZero analysis DC Transfer Function InputOutput Impedance and gain TEMPERATURE Circuit and Part Temperature sweeps SENSITIVITY Works for AC, DC, Transient and OP analyses using Perturbation analysis Design Validation Automatic Userdefined 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 Builtin 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 (Builtin)
Analog Behavioral Modeling
Analog C Code (AHDL) Models
Hybrid C Code (AHDL) Models
 DigitaltoAnalog Node Bridge
 AnalogtoDigital Node Bridge
 DigitaltoReal Node Bridge
 RealtoAnalog Node Bridge
 AnalogtoReal Node Bridge
 Voltage Controlled Digital Oscillator
Real (SampleData System) C Code (AHDL) Models
 ZTransform 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
 SetReset Flip Flop
 D Latch
 SetReset Latch
 State Machine
 Frequency Divider
 RAM
 Digital Source
 MIDI Digitally Controlled Oscillator
Salt Models (with model source code)
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: 32bit version of SPICE for DOS, 64bit 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 mixedsignal fault and test diagnosis, automated setting/recording of electrical measurements across designs with stress alarms, schematicless device sweeping, magnetics design and synthesis, DSP simulation and firmware.