Signal Integrity of Coplanar Waveguides versus Microstrip Interconnects for Clock Distribution

Abstract

This thesis investigates the use of Grounded Coplanar Waveguide (GCPW) interconnects,commonly employed in monolithic millimeter-wave circuits, versus microstrip interconnects for distributing digital clock signals on printed circuit boards (PCBs) with the goal of improving electromagnetic compatibility (EMC) and signal integrity (SI). Two prototype PCBs, one using microstrip traces and the other using GCPW traces, were designed and fabricated using identical materials and layout constraints. Both designs were simulated and measured in the frequency and time domain to evaluate their performance in clock signal splitting and isolation from adjacent transmission lines. Results show that the GCPW-based PCB outperforms the microstrip design in the frequency range from 300kHz to at least 6GHz. The GCPW circuit demonstrated a superior suppression of electromagnetic coupling and crosstalk to adjacent nets, reduced clock skew, lower reflection, and minimized signal attenuation. After propagating through the clock distribution network, clock signals at the output ports of the GCPW PCB displayed greater signal integrity and a higher isolation between output ports than the microstrip PCB throughout the measured spectrum. Crosstalk measurements taken on a net adjacent to the clock distribution circuit, while clearly quantifiable on the microstrip PCB, were nearly undetectable on the GCPW PCB. This study supports the use of GCPW structures over microstrip for high-performance digital clock distribution to improve EMC and SI.