Passive impedance equalization of high speed serial links

In some embodiments a passive impedance equalization network for high speed serial links is described. The impedance equalization network includes at least one stepped impedance transformer near points of impedance discontinuities. The impedance discontinuities may be at an interface connection between two circuit boards. The impedance discontinuities on a circuit board may be at a die-package interface and/or a package-board interface. The stepped impedance transformer may be formed in a package trace, a board trace or both. Forming the stepped impedance transformers in the traces requires no modification to existing package/board design methodology or technology. The stepped impedance transformers can provide impedance matching over a range of frequencies. To account for modeling errors in the design of the stepped impedance transformers integrated circuits transmitting data over the serial link may include active circuitry to select an output/input impedance for transmitters/receivers. Other embodiments are otherwise disclosed herein.