Twisted differential transmission line on high-speed printed circuit board for enhanced Immunity against crosstalk and radiated emission

Abstract

In this paper, twisted differential transmission line (TDL) is fully characterized with both experiments and simulations. The methodology of using G-S probe for the measurement of TDL is proposed and verified. With this methodology, the transmission characteristics of TDL including the propagation constant and the differential impedance are measured. From the results, its capability to transmit over GHz signal is verified. Moreover, TDL is modeled by a simple equivalent circuit. With this model, TDL can be analyzed with circuit simulator. TDL is also analyzed with full-wave simulations, which shows good agreement with experimental data. Therefore, transmission line properties of TDL including differential impedance and phase velocity can be determined in the early stage of design with this simulation. The enhanced immunity of TDL against crosstalk and radiated emission is demonstrated experimentally. TDL is compared with another differential transmission line structures showing its superiority in terms of the immunity against crosstalk and radiated emission. Offset TDL (O-TDL) and Vertical TDL (V-TDL) are newly proposed verified with experiments. With O-TDL, the immunity against crosstalk can be further improved. In addition, V-TDL enables reduced routing area while maintaining performance. Finally, the design guide for using TDL is suggested.