10-40 GHz design in SiGe-BiCMOS and Si-CMOS - linking technology and circuits to maximize performance

This paper reviews the relevance of the widely used device metrics f/sub T/, f/sub max/ as well as the recently introduced device metrics f/sub A/ and f/sub cross/ for broadband circuit design. Usually, IC processes are benchmarked on the basis of their f/sub T/ and f/sub max/. For most circuit applications however, there is only an indirect relation between f/sub T/, f/sub max/ and circuit bandwidths. Since the differential pair amplifier is a key building block in broadband circuits, the metric f/sub A/ provides a nearly direct relation to broadband circuit performance. This is demonstrated via the maximum operating frequency of a current-mode logic frequency divider, processed in 3 generations of a BiCMOS process. Metric f/sub cross/ is valuable for the design of circuits employing a cross-coupled differential pair as active negative resistance, such as in LC-VCOs. The metrics can be expressed in terms of transistor parameters (e.g., R/sub b/, C/sub bc/...), allowing to derive a link between circuit performance and technology. Based on our experience, we evaluate IC processes on the basis of f/sub T/, f/sub A/ and f/sub cross/ rather than f/sub T/ and f/sub max/.