Figure 10: Shown are the significant insertion loss and crosstalk specifications as a function of frequency for the 10128419- 101LF header. (Image source: Amphenol)
impedance and bandwidth. SI specifications include attenuation, velocity factor, return loss, insertion loss, and crosstalk. An example of a coaxial cable is Times Microwave Systems’ LMR-400-ULTRAFLEX 50 Ω low- loss cable, rated for indoor or outdoor operation at 6 GHz. Its frequency-dependent attenuation is 0.05 dB/ft. at 900 megahertz (MHz) and increases to 0.13 dB/ ft. at 5.8 GHz. Its propagation velocity, a specification used when dealing with reflections, is 80% of the speed of light (a velocity factor of 0.8). Reflection and transmission losses are length-dependent and are not given in bulk cable specifications.
Components such as connectors are specified somewhat differently. The Amphenol Communications Solutions 10128419-101LF 112-position male header connector is intended for backplane use. It is rated to handle digital signals with a maximum bit rate of 25 to 56 Gbps. Its contacts have a characteristic impedance of 92 Ω. As a multiconductor connector, its insertion loss and crosstalk specifications are critical (Figure 10). These are typical SI specifications associated with interconnect components.
Conclusion SI must be considered throughout the design process for high-speed systems such as AI data centers. Many factors can affect SI, and designers must account for them all to mitigate their effects. SI can be maximized with the proper PC board trace layout and appropriate conductors and connectors.
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