The Advantages of Substituting Decoupling Capacitors on PWB with Embedded Capacitance Technology

This paper discusses the importance of power delivery network (PDN) with minimal level of impedance on the printed wiring board (PWB) with multi-Gigabit signal transmission and the effect of embedded capacitance material (ECM) in reducing the PDN impedance across the wideband range. The advantages of applying ECM versus discrete decoupling capacitors on compact PWB in terms of physical real estate and power integrity are also introduced. The work to investigate the feasibility of ECM substituting the discrete decoupling capacitors was implemented in two stages. In the first stage, the power integrity simulation was performed to analyze the PDN impedance of the power net of interest. In the second stage, the physical measurement of simultaneous switching noise (SSN) of the power rail of interest and the eye diagram of the Peripheral Component Interconnect express (PCIe) signal at 2.5 Gbps are carried out using oscilloscope. The jitter and SSN are diminished by 19 % and 9.3 % respectively when the PWB is laminated with ECM. Hence, the ECM is capable to serve as an alternative to the decoupling capacitors and facilitates the miniaturization of the PWB.

I. Introduction

It is imperative to maintain the impedance of power delivery network (PDN) on the printed wiring board (PWB) at minimal level to reduce the simultaneous switching noise (SSN) caused by the transient current of the components hooked up to the power net. With reference to Eq. (1), the transient current of the component convolves with the PDN impedance and produces SSN. The SSN on the power net, i.e., a power integrity issue, in turn intensifies the jitter of the signal transmission on the PWB, i.e., a signal integrity issue [1]. This eventually causes data error or even failure in the digital communication system. $$\begin{equation*} \Delta V=\Delta I\times Z_{PDN} \tag{1} \end{equation*}$$ where is the SSN, is the transient current, is the PDN impedance.