Transmission line losses—driven by skin effect and dielectric properties—play a critical role in degrading high-speed signal integrity and eye performance.
Transmission line loss directly affects eye diagram quality, with around −12 dB at Nyquist marking the limit before signal integrity rapidly degrades without equalization.
Eric is a professor in the EE department at Colorado University, Boulder and a Fellow at Teledyne LeCroy. He has a BS in Physics from MIT and a PhD in Physics from the University of Arizona, Tucson. He enjoys DesignCon and writing for SI Journal.
Broad dips in S-parameter plots typically result from stub resonances, where reflected signals interfere with the main signal path and reduce transmission at specific frequencies.
A monotonic drop-off in S21 indicates increasing signal attenuation with frequency, typically caused by dielectric and conductor losses in the interconnect.
Ripple patterns in S-parameters are caused by reflections from impedance discontinuities, with ripple spacing determined by interconnect length and ripple magnitude driven by impedance mismatch.
Sharp dips in S-parameter plots often indicate coupling to high-Q resonant structures, where specific frequencies are absorbed by PCB cavities or floating interconnects.
Choosing between a 50 Ω and 1 MΩ oscilloscope input depends on signal bandwidth, cable impedance, and voltage level to ensure accurate and safe measurements.
Following key measurement best practices—anticipating results, understanding instrument limits, defining objectives, and validating consistency—helps ensure accurate oscilloscope measurements.
FFT analysis converts time-domain oscilloscope data into a frequency-domain spectrum, revealing the signal’s underlying sine-wave components and interference sources.
Understanding the differences between reflection coefficient, return loss, transmission coefficient, and insertion loss eliminates common S-parameter confusion.
