- Introduction
- QaSimDemo Applet
- Usage
- Example
- Bipolar Transistor States
- Small-Signal Models of Capacitances
- Hints & FAQ
- References

Attention:

This Demo works only with old Java-Workshop (JDK1.0).

At the beginning of a design process the designer has to verify which circuit structure is suitable for a given purpose. At this stage numerical and symbolic analysis are of little use. There are no numerical values for conventional simulation with programs like SPICE and a Symbolic Analysis would produce large symbolic expressions. No further approximation of these expressions can be performed due to the lack of numerical values.

An experienced designer however, is able to analyze the
behavior of an unknown circuit. The Qualitative Analysis
reproduces this ability on computers by introducing qualitative
states such as *positive*, *zero*, or
*negative*.

The applet is a graphical user interface to the QA Server. The QA
Server performs the computations and runs on the same computer
(www.nst.ing.tu-bs.de,
SUN Ultra450) as the WWW Server.

With this demo version DC and Small-Signal Analyses of the following circuit structure can be performed:

The QA Server uses this netlist:

Astable Multivibrator * R1 1 2 + R2 2 0 + R3 4 0 + R4 5 0 + R5 1 3 + C1 4 5 + IC = - Q1 3 2 4 QN Q2 1 3 5 QN VS 1 0 + .MODEL QN NPN ( QADCAC=MINB ) .END

QaSimDemo Applet
The main window can be opened again after quitting by pressing the button. |

Usage:

**Options & Defaults:**-
*Expand Node and Loop Equations*- Generate additional node and loop equations
*Display System of Equations*- Display the qualitative system of equations
*Display Solved Equations*- Show the equation numbers while solving the system of equations
*Vector Pointer / Vector Array*- Switches between different internal data structures

**Analysis:**-
*Start DC Analysis*- Start a DC Analysis. You must set the
states of the nonlinearities
(transistors) with
*Set Nonlinears*before. With*Use Initial Conditions*the initial conditions of the dynamic elements are taken into account. *Start Small-Signal Analysis*- Start a Small-Signal Analysis. You must set the
states of the nonlinearities
(transistors) with
*Set Nonlinears*and the small-signal models of the dynamic elements (capacitors) with*Set Dynamics*before. With*Check Operating Point*an additional DC Analysis validates the operating point.

**Console Messages:**- You can watch the solving process here. If the window
*Error Message*appears displaying an equation, this equation leads to a contradiction.

Example (DC Analysis):

- Choose
*Analysis* - Click on
*Set Nonlinears*, the window*States of Nonlinearities*appears - Click on
*Apply* - Click on
*Done* - Click on
*Start DC Analysis*, the window*Results*appears - Click on
*Select All* - Click on
*Display* - The result will be shown

**Interpretation of the Result:**

The choosen states of the transistors are valid. There are three
possible states of the circuit caused by the uncertain branch
voltage `U(C1)`.

OFF | Off |

FON | Forward On |

RON | Reverse On |

FST | Forward Saturation |

RST | Reverse Saturation |

Small-Signal Models of Capacitances:

OL | Open Loop |

RS | Resistance |

SC | Short Circuit |

Hints & FAQ:

The FAQ (hopefully) answers the most
common questions.

Please direct additional notices, questions, and suggestions to
webmaster@nst.ing.tu-bs.de!

References:

- M. Thole, J. Meise, E.-H. Horneber,

**Qualitative Analysis of Nonlinear Dynamic Circuits**,

Proceedings of 2nd International Conference on Intelligent Systems Engineering, Hamburg, September 1994 - M. Thole, J. Meise, E.-H. Horneber,

**Evaluating Possible States of Nonlinear Dynamic Networks by Use of Qualitative Analysis**

Proc. 3rd Int. Workshop on Symbolic Methods and Applications to Circuit Design (SMACD'94), Seville, October 1994 - M. Thole, E.-H. Horneber,

**Qualitative Analysis of Analog Circuits with Expanded Node and Loop Equations**,

Proc. 3rd IEEE Int. Conf. on Electronics, Circuits, and Systems ICECS '96, Rodos, October 1996

aktualisiert: 13.10.2010

Verantwortlich: Michael Hinz

Feedback an: m.hinz@tu-braunschweig.de