The millimeter-wave frequency range provides very large bandwidths (30-300 GHz) capable of supporting ultra high speed (more than 1 Gb/s) wireless links. The wavelengths at these frequencies are very short, giving researchers opportunities to reduce the chip area for wireless transceivers. These encouraging factors together with the availability of advanced CMOS processes (with gate lengths shorter than 100nm) open up the possibility of integrating complete millimeter-wave transceivers using relatively inexpensive silicon technologies, suitable for the consumer market.

One of the key challenges of millimeter-wave circuit design is the complex physical effects that occur at high frequencies. Researchers in IME have developed a new automated modeling methodology for passive devices such as transmission lines and inductors to address to these challenges. The models are continuously scalable with device dimensions, which facilitate the ease with which a millimeter-wave circuit designer can optimize their designs.

The model is built upon a core network, which includes a flexible topology so that the device can be modeled up to an arbitrarily high frequency. This is accomplished by simply adding more series and shunt sections to the model in Fig. 1. The other benefit of the new model topology is that the equations of its characteristics are far simpler than previously developed models.

Fig. 1. The new millimeter-wave passive component model topology.

A new feature of this model is that it is scalable with device dimensions. It describes transmission lines with varying lengths and widths, and inductors with varying diameters. For example, Fig. 2 shows two inductors with different diameters fabricated in a CMOS process. In the past, unscalable millimeter-wave modeling methodologies required a separate model for each device dimension. This new millimeter-wave scalable modeling methodology greatly increases the speed and effectiveness of creating a complete model library ready for millimeter-wave circuit design.

Fig. 2. Two millimeter-wave inductors fabricated in a CMOS process with different diameters.

Fig. 3a shows the measured and modeled inductance of lumped inductors (such as those shown in Fig. 2) with varying diameters. Fig. 3b shows the measured and modeled characteristic impedance of microstrip transmission lines with varying widths. It can be seen that one model is able to accurately describe the characteristics of millimeter-wave passive devices over a wide frequency range and with scalable device dimensions.

Fig. 3a. Measured (points) and modeled (lines) modeled inductances.	Fig. 3b. Measured and transmission line characteristic impedances

Further details of this work can be found in the December 2008 issue of IEEE Transactions on Microwave Theory and Techniques.