Improvements of Time-Domain Transmission Waveform and Eye Diagram of Serpentine Delay Line Using Open-Stub Type Guard Traces in Embedded Microstrip Line

The utilization of guard traces with two grounded vias at both ends to improve the time-domain transmission (TDT) waveform and eye diagram for a serpentine delay line has been investigated. However, it is not easy to accomplish because the position of the pad of a grounded via is surrounded by a serpentine trace. This is especially true for normal manufacturing technology, where the size of via pad is larger. Therefore, this paper proposes the use of open-stub type guard traces (OSGTs), to reduce crosstalk noise in the TDT waveform and eye diagram of a serpentine delay line, in an embedded microstrip structure. The OSGT, i.e., the guard trace, at one end is a grounded via and at the other is open-ended. The crosstalk reduced efficiency for using OSGTs is almost the same as when using two-grounded-via type guard traces on the serpentine delay line in the time-domain. This is because, the open-end of the OSGTs leads to the noise cancellation mechanism. A graphic method was used to illustrate the noise cancellation mechanism and ringing crosstalk noise generation on the TDT waveform. Two useful design graphs were used to evaluate the maximum flat voltage level of a laddering wave. Based on HSPICE simulation, it was demonstrated that the utilization of OSGTs can significantly reduce the original TDT crosstalk level, thereby greatly improving eye opening and jitter. Finally, this paper also performs time-domain measurement and 3-D full-wave simulation to validate the proposed analyzes.