Intusoft's ICAP/4 Circuit Simulator Provides
Unique GFT Approach to Closed Loop Measurement

Gardena, CA (April 14, 2003) -- Intusoft announced today a unique offering based on a mathematical model of a control system called, "General Feedback Theorem" (GFT). Dr. R. David Middlebrook with the California Institute of Technology developed the theorem. The principle arises from application of a bi-linear transform, originally described by Bode in 1945. Middlebrook extended Bode's work with his Extra Element Theorem (EET), then successively by applying the EET within a control loop using voltage and current sources instead of impedances. The GFT can be used to measure open loop control system characteristics, but while the loop is closed, thereby preserving correct loading and DC bias along the path.

Intusoft's ICAP/4 Windows analog, mixed-signal and mixed-engineering systems simulation offering has incorporated GFT models and associated scripts that provide many advantageous tasks for designers. The unique SPICE scripts enable special interaction between the IsSpice4 simulation engine and ICAP/4's "IntuScope" waveform viewer. The offering furnishes all combinations of single and dual injection GFT elements using 28 special models, 5 GFT simulation templates and 35 example drawings. The drawings also include hierarchical topologies used to make the models. Dr. Middlebrook authored the GFT manual that includes all associated GFT equations, and walks you through the example circuits included in the web download,

Many switch-mode power supply (SMPS) circuits do not exhibit an appropriate place to break a closed loop topology because the control circuitry is inaccessible. For instance, breaking the loop to measure open loop gain is disruptive and removes natural loading at the cut point. Moreover, the DC operating point is difficult to establish with the loop open. But with GFT elements, a fast and viable means of measuring SMPS closed loop performance is achieved without disrupting the intended loop configuration.
The GFT application is part of Intusoft's (IsSpice4) simulation kernel, ICAP verification environment and associated libraries, running on Windows NT and XP platforms.
Established in 1985, Intusoft designs, develops and markets award-winning software to electronics industries worldwide. Its products comprise a breadth of applications geared for analog and mixed-signal circuit design, analysis and test automation. Information on Intusoft and its products is provided at:


For Further Information Contact:

Tim Ghazaleh
Director of Marketing, Intusoft
Direct (925) 600-7445
Tele (310) 329-3295 Fax (310) 329-9864