Optimizing the Full Mixed-Mode Performance of a Differential Microstrip Interconnect with a Right-Angle Bend by using Two Symmetrical Bumps

Abstract

Differential interconnects are widely used for high-speed serial data transmission in modern high-performance computer platforms. Differential signaling handle noise better than single ended signaling. However, physical asymmetries and discontinuities in differential links can cause that a portion of the differential energy is converted into common mode (CM) energy, which is perceived as noise at the receiver. This mode conversion in differential interconnects leads to electromagnetic (EM) interference and EM susceptibility, limiting high data rates. In this paper, a microstrip differential interconnect with a severe discontinuity, a right-angle bend, is optimally compensated by using two rectangular length-match bumps. Our formulation allows the efficient optimization of the full set of mixed-mode (MM) S-parameters of the differential interconnect. It uses a smart combination of pattern search and Nelder-Mead to optimize the MM performance considering several starting points. The interconnect MM performance before and after optimization is shown, confirming a very significant performance improvement.