Characterization of interconnections performances for high speed digital boards: a frequency/time domain approach

On the modern digital equipments, characterized by continually increasing bandwidth requirements, the electrical properties of the printed circuit board interconnections affect and limit the quality of the traveling digital signals. This impacts on the electro-magnetic compatibility (EMC) performances of the system, because corrupted signals can easily increase the emissions from the system. Specific dielectric materials with low dielectric losses must be used for board manufacturing, in order to transmit digital signals with a high frequency harmonic content on longer distances. Consequently it is important to characterize, as function of the bit rate and the rise/fall time of the transmitted signal, the attenuation and deterministic jitter due to the dielectric material building up the board. To do this, one must separate (de-embed) from the measurements the effects of the adapters, used to connect the test board at the measuring instrument. The proposed de-embedding method uses a vector network analyzer with time domain option and only two traces, laid-out on the test board, with different lengths. The technique is validated by comparing the measured values with those coming from simulations.