The IFFT program

The IFFT program analyzes linear circuits, computing transfer functions in Laplace transform. From the transfer functions, in a ratio-of-polynomials form, the program can compute poles and zeros an plot frequency response graphs. The program was developed as a tool for fast verification of continuous time filter designs. It is also useful for other purposes, as:

• Stability analysis by direct poles and zeros calculation.
• Studies about frequency compensation of amplifiers.
• Studies about compensation of operational amplifier GB and input and output impedance effects in filters.
• Studies about the effects of parasitic capacitances and resistances in filters.
• Monte Carlo analysis and study of the effect of component variations.

The EdFil editor is included in all versions. It provides easy circuit entry in schematic form, requiring only a minimum of information, typing, and care with the schematic layout

The use of the IFFT program is free for academic, noncommercial purposes. For commercial use, please contact the author.

Select a version to download below:

The files are compressed in the "zip" format.

• Windows version 1.7. Almost identical to version 1.6, for Windows.
• DOS version 1.6. Transformer with "K".
  
• DOS version 1.5b. Accepts operational amplifiers with 4 terminals (floating output) and comments. Transconductors may have common-mode transconductance. (old)
• DOS version 1.4a. The most tested version. Includes the EdFil editor and an utility to compute time-domain responses by the inversion of the Laplace transform (AnaTran). (old)
• Sun Unix version 1.0. Includes the executable IFFT and EdFil programs and the manual file. (old)
• HP-UX version 1.0. Includes the executable IFFT and EdFil programs and the manual file. (old)
• Linux version 1.0a. Requires X11 and XView. Included are the binary files for IFFT and EDFIL and the manual. (old)

The DOS versions can be executed under varios operating systems using the DOS emulator DosBox.

The picture above shows the simulation of an active filter realizing a 5th-order elliptic filter. The frequency response is as expected, but the structure has a natural frequency at zero, that appears as a pole-zero cancellation there. This may be a problem in an actual construction, because the circuit has undefined DC voltages or currents somewhere on its structure.

Developed and Maintained by Antonio Carlos M. de Queiroz
Last update: 2/7/2012.