CMOS Inductor design
Inductor design tools
ASITIC
This is a program that is freely available from the University of California,
Berkley website. In the words of the author, “ASITIC is a CAD tool that aids
RF/microwave engineers to analyze, model, and optimize passive metal structures
residing on a lossy conductive substrate”. This includes inductors, transformers,
capacitors, transmission lines, interconnects and substrate coupling analysis.
ASITIC is an Unix based graphical program which runs under the X windows
environment. Typing asitic on the shell prompt brings out a layout screen where the user
can specify the geometry of the object under test. It supports different kinds of
geometries like the square and even non-traditional shapes like the polygon. There are a
series of simple commands that help the user layout the spiral and help one manipulate it.
The next important step is editing the technology file, which specifies the IC
process. In the technology file, specifying the size of the FFT specifies the resolution of
the analysis. Different kinds of simulations can be done and the relevant parameters like
inductance, quality factor and self-resonant frequency determined at a particular
frequency. The program is relatively fast and simple which gives a good first cut for the
different design parameters.
Agilent ADS
This is a complete suit from Agilent, which does different types of simulations It
uses a “method-of-moments” based engine to run electromagnetic simulations of 2D
structures. The technology file for the process can be input and solved one time and
reused with different geometries. This saves a lot of time when testing different
geometries under a single process.
The spiral can be either specified by selecting from a large collection of standard
geometries or the user can draw the spiral using traces. With this option the user has
considerable room to test a wide variety of spirals and is not limited by the ones available
in the library.
The results can be observed either as Smith charts or any of the other standard
formats. Animations of currents and charges help the user to interpret the results better.
For example, effects such as current crowding can be observed visually and better
understood.
The small disadvantage with this program seems to be the long simulation time
depending on the resolution of the mesh used for analysis.
SONNET
SONNET is a suite of products which provides high-frequency planar
electromagnetic analysis for different products. It uses a modified method of moments
analysis based on Maxwell’s equations to perform a true three dimensional current
analysis of predominantly planar structures. Em, the electromagnetic engine, computes S,
Y, or Z-parameters, transmission line parameters (Z0 and Eeff), and SPICE equivalent
lumped element networks.
17
The suite includes a number of tools like emvu and patvu which are visualization tools to
help the user better interpret the results.
SONET software is also used for design and analysis of high-frequency circuits,
distributed filters, transitions, RF packages, waveguides and antennas. Some of the
features include modeling of microstrip lines, modeling of via analysis along with some
packaging effects and spiral inductors.