10-40GHz 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_T, f_max as well as the introduced device metrics f_A and f_cross for broadband circuit design. Usually, IC processes are benchmarked on the basis of their f_T and f_max. For most circuit applications however, there is only an indirect relation between f_T, f_max and circuit bandwidths. Since the differential pair amplifier is a key building block in broadband circuits, the metric f_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_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_b, C_bc, ...), allowing to derive a link between circuit performance and technology. Based on our experience, we evaluate IC processes on the basis of f_T, f_A and f_cross rather than f_T and f_max.