Characterization of differential interconnects from time domain reflectometry measurements

Differential signaling schemes are a common approach to achieving higher noise immunity for critical signals in a high-speed digital design. A differential pair constitutes a set of coupled transmission lines and, therefore, can be modeled and simulated as such. Short differential lines can be modeled using coupled LC matrices, but a distributed model is required for longer lines. In this article, a technique for extracting such a distributed coupled line model from time domain reflectometry (TDR) measurements is presented. This model can be easily utilized in a SPICE simulator, making it extremely useful for high-speed differential interconnect modeling and simulation. The resulting accurate models help the designer to achieve a better understanding of the differential interconnects, resulting in higher performance system design.