Signal Integrity and Radiated Emission of High-Speed Digital Systems

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Measurement and Modeling

Signal Integrity (SI) is a primary concern for system functionality and Electromagnetic Compatibility (EMC) compliance, and allows a product to achieve the required certification to be legally sold. Printed Circuit Boards (PCBs) are the physical structures used for the mechanical support of transmission lines and connect components. Signal integrity is based on how efficiently the information propagates through a transmission line, and can be verified by measurements in the time and frequency domains. A direct relationship exists between time-and frequency-domain measurements, and is provided by Fast Fourier Transform (FFT) and Inverse FFT (IFFT), respectively.

Two key instruments useful for extracting circuit parameters regarding interconnects and discontinuities occurring in high-speed digital systems are presented. The first is the Time-Domain Reflectometer (TDR) which performs measurements in the time domain, and the second is the Vector Network Analyzer (VNA) which performs measurements in the frequency domain. The advantage of performing time-domain measurements is that the effects of a discontinuity along the interconnect on signal integrity can be directly observed, and models of the parasitic elements can be developed for the switching time of interest. The advantage of performing frequency-domain measurements is that resonance effects at some frequencies can be determined and appropriate models for components can be developed.

The theory of ...