Guard Trace Design for Improvement on Transient Waveforms and Eye Diagrams of Serpentine Delay Lines

This paper investigates the utilization of the guard traces to improve the eye opening and jitter for serpentine delay lines. It is found that the guard trace can reduce the original time-domain transmission (TDT) and time-domain reflection (TDR) crosstalk noises by more than 50%, if shorted by only two grounded vias at both ends of the trace. The time domain analysis as well as the associated simple circuit modeling is presented to explain the occurrence of noise cancellation mechanism on the guard trace. In addition, narrow signal trace is proposed to improve the TDR waveform by compensating the impedance mismatch due to the inserted guard traces. Finally, the HSPICE simulation and time-domain measurements of crosstalk noises, TDR/TDT waveforms, and eye diagrams are performed to validate the proposed analysis and design.