Samuel Connor

Compact Configuration for Common Mode Filter Design based on Planar Electromagnetic Bandgap Structures

A planar electromagnetic bandgap configuration of a compact common mode filter that is laid out on printed circuit board is studied. This filter is used to mitigate the common mode noise traveling on high-speed differential signal traces. These differential signal lines may be connected to I/O connectors and cables and small amounts of common mode noise can result in significant electromagnetic emissions. The filter is obtained by a very simple planar geometry based on the electromagnetic bandgap structures. A cavity made by a rectangular/square patch (together with a solid plane underneath) has a well known and predictable resonant behavior; the coupling between the differential pair routed on top of the patterned plane and the patch cavity, occurring when the traces cross the gap between adjacent patches, is used to reduce the energy associated with the propagation of the common mode noise. The properties of this filter are studied taking into account the layout of a real differential microstrip and the number of gap crossings. A compact configuration is proposed. Time domain simulations validate the suggested layout approach.

Common mode filtering performances of planar EBG structures

This paper approaches the filtering behavior of Electromagnetic Bandgap (EBG) structures. The transfer function, in terms of S-parameters, of a single ended and a differential microstrip line referenced to an EBG plane are considered: the notches (causing signal attenuation) and flat regions (causing signal propagation) are related to the geometry and characteristics of the EBG structure and can be designed to filter out unwanted harmonic components of the signal. A different EBG-like structure is proposed and its performances analyzed.

EMI Emissions from mismatches in High Speed Differential Signal Traces and Cables

The use of so-called differential signaling for high speed signals has become very common in todays high speed system designs. While this signal strategy allows better data quality and signal integrity, there are some significant EMC and signal integrity issues that are not readily apparent. This paper demonstrates that a significant amount of common-mode current can be created when the two legs of the differential signal are skewed in time, or if the rise and fall times of the signals differ. These common mode currents can impact the EMC performance, causing significant levels of emissions unless careful design consideration is given to shielding and common-mode (ground) current return.

Design of a Common Mode Filter by Using Planar Electromagnetic Bandgap Structures

In this paper, an embedded electromagnetic bandgap structure is proposed for harmonic filtering of differential signals undesired common mode components. Rather than use lumped circuit components and likely causing some degradation to the intended high speed differential signal, the embedded planar common mode filter causes no degradation to the intended signal, and enhances the signal integrity and electromagnetic compatibility performance of the system. Single ended and differential traces are considered and the impact of the common mode filtering is measured in terms of mixed mode scattering parameters and eye diagram metrics. The systematic procedure to design such a structure is outlined, and its design robustness is also verified.

The effect of decoupling capacitor distance on printed circuit boards using both frequency and time domain analysis

This paper demonstrates the effect of decoupling capacitor distance on the amount of EMI noise created at an ICs power pin. As the distance is increased, the amplitude of the noise is increased if the capacitor has been attached to the printed circuit board (PCB) with a low inductance connection. This effect is most apparent when the dielectric thickness of the PCB is greater. Furthermore, this paper demonstrates the need to do this type of analysis in the time domain and not the frequency domain

Return via connections for extending signal link path bandwidth of via transitions

This paper discusses a fast and accurate way to assess the impact of signal vias where the return current must change reference planes, including the effect of a return current via placed various distances from the signal via. The equivalent circuit includes capacitance of the via anti-pad as well as cavity effects.

Noise coupling between signal and power/ground nets due to signal vias transitioning through power/ground plane pair

Signal vias are often used to move a signal from one PCB layer to another. As a result, these vias can penetrate power/ground plane pair and cause noise coupling (crosstalk) between signal and power/ground nets. This paper studies the noise coupling mechanism using a segmentation approach combined with a via capacitance model and a plane-pair cavity model. Noise coupling from signal to power/ground, and vice versa, is demonstrated in the modeling results.

Comparing FSV and human responses to data comparisons

The feature selective validation (FSV) method was developed with the specific goal to mirror the approach taken by engineers when assessing data presented visually during the validation of computational electromagnetics. The FSV (feature selective validation) technique has been demonstrated to have good agreement with the human survey results for a number of different data sets. Survey results for data sets in good agreement show a very small standard deviation, however, data sets with fair agreement have a significantly higher standard deviation.

Experimental validation of common-mode filtering performances of planar electromagnetic band-gap structures

An experimental validation of an electromagnetic band-gap (EBG) based common mode filter is given in this paper. The proposed layout technique is based on planar EBG structures altered by removing the connecting bridges between adjacent patches. The patches are properly dimensioned for ensuring the presence of frequency notches at the frequencies that should be filtered in the common-mode transfer function. The notch frequency is associated with the first resonant mode of the patch.

Analysis of noise coupling result from overlapping power areas within power delivery networks

Large area fills or entire planes constitute the backbone of the power delivery network in multi-layer printed circuit boards (PCBs). The overlapping of power areas at different voltages, though, may cause coupling among them. Full wave methods can be used to model these types of structures, and the coupling effect can be accurately analyzed by means of the finite element method (FEM), finite difference time domain (FDTD) and others. However, full wave methods are usually time consuming. In this paper, a cavity model approach is proposed to analyze the noise coupling among plane pairs in multi-layer configurations. The cavity model has analytical expressions for the impedance (Z) matrix associated with ports defined on regularly-shaped planar circuits and it is computationally efficient. The combination of such an approach with the segmentation method allows the extension of the analysis to irregularly shaped and multi-layer structures. A multi-layer PCB with three power planes is analyzed in this article by means of the proposed cavity model approach as well as a full wave FEM method. A comparison between the simulation results obtained with the two different methods is finally provided. Keywords-PDN; cavity model; power bus; overlapping power area; segmentation method; multilayer PCB