High Signal Integrity Transmission Line Using Microchip Capacitors and Inductors

In order to improve signal integrity (SI) in PCB traces, or transmission lines, impedance matching techniques have been widely used so far. However, in the frequency domain of more than 5 GHz, it becomes difficult to make impedance matching designs in printed circuit boards (PCBs). In this paper, we propose a novel trace structure called "Capacitor Inductor Segmental Transmission Line (CL-STL)", in which not impedance matching but "mismatching" is used to improve SI. In the CL-STL, microchip capacitors and inductors are connected to the transmission line to make impedance mismatching points and to generate reflection waves intentionally, and those reflection waves are superposed onto the original distorted wave to get it into shape. In the CL-STL design, we make use of the cuckoo search algorithm, which is one of the swarm intelligence optimization algorithms, to solve the combinatorial explosion problem of microchip capacitors and inductors. We apply the CL-STL to an 8 Gbps PCB trace and obtain a high SI eye-diagram, the height and the width of which are improved by 6.9 and 1.44 times, respectively.