Study of TDR Impedance for Better Analysis to Measurement Correlation

SI engineers usually build PCB test coupons and perform cross-sectioning and material properties extraction, and then do design optimization. But designing transmission lines on PCB with good analysis to measurement correlation is really challenging. Although there are some systematic approaches which can be applied to a broad range of applications for highspeed digital designs, it is found that in the validation process, there is always several-ohm mismatch in the comparison of TDR impedance between simulated and measurement results. This degrades engineers' confidence about high-speed design. Taking a real case as an example, this paper is trying to analyze which factors have influence on the trace impedance correlation and showing step by step how the agreement can be improved.