High speed PCB designing for EMC in biomedical systems

Abstract

High speed data (Gbps) demand for next generation high performance computing devices makes electromagnetic compatibility (EMC) and signal integrity (SI) crucial for modern medical product design. EMC and SI technologies on the printed circuit board (PCB) are the bottlenecks to achieve such high data rate. EMC and signal integrity are major challenges in PCB, which might itself inject switching noises, thereby decreasing the EMC performance of electronic equipment, especially sensitive equipment requiring high precision, such as medical instruments. In this research, we focus on four major problems in PCB, i.e. fiber weave effect, split plane effect, SSN and finally EMC problem. Four solutions are proposed for reducing these effects on PCB level and adversity effect to increase the EMC performance of the system. The first solution for reducing the phase difference between the differential pair is explored, studied, and simulated on IBIS-AMI models and a solution is proposed. Fiberglass and epoxy-based dielectric substrates are ubiquitous in manufactured printed circuit boards. Their construction usually involves various woven fiberglass fabrics saturated with epoxy resin. These two materials have different electrical properties; hence, as the data rate increases and structure feature-size decreases, the fiber weaves in the substrates can have profound impacts on the effective dielectric constants of printed circuit boards, which can cause unforeseen degradations in signal integrity. This work proposes a systematic way of modeling the fiber weave effect on high-speed interconnects over low-cost substrates, and also presents a statistical analysis of the impact of the fiber weave effect on intra-pair skew of differential microstrip lines. The second solution is proposed to overcome the split plane crossing problem for high speed interconnects. It is a geometry based method which is very effective during slot crossing. When a high frequency signal crosses the split plane gap, the return current path inductance is increased during the crossing of the plane. The inherent inductance leads to two EMC problems, creation of a radiating dipole and increased magnetic coupling. An efficient radiating dipole is created by high frequency current passing through the inductance, developing a voltage that appears across the two parts of the plane, each of which has a high capacitance. The third proposed method is directly related to the EMC parameter of the system which is very effective during the noise condition, i.e. plane coupling is used to dramatically improve the EMC parameter of the system. The last method is proposed to reduce SSN effect on the system without adding any extra cost to the product. In this work, power supply distribution network noise caused by simultaneous switching noise at printed circuit board level is controlled effectively by the use of integrated capacitors between the power planes at data speed 2.133Gbps. In the present research work, a test board was designed for improving EMC performance of the medical system by using the proposed method. Simulation results were compared with the real measurement results of the test board, which is the right approach to correlate the results. These methodologies could be treated as handy references and general guidelines applicable to different PCB designs and could result in significant improvements of overall signal integrity performance and EMC in high speed medical system links.