Michael Cracraft

EBG-Based Common-Mode Microstrip and Stripline Filters: Experimental Investigation of Performances and Crosstalk

The aim of this study is to analyze from a modeling and experimental point of view the filter effectiveness and the crosstalk among signal traces crossing the same common-mode filter based on electromagnetic bandgap structures in a modern server design configurations. Both microstrips and striplines are considered in the study, detailing the differences among them in the design step as well as in filter geometry and response. Simulation models and experimental setups are carefully described, and the numerical and measurement results are compared and discussed.

Removable EBG-Based Common-Mode Filter for High-Speed Signaling: Experimental Validation of Prototype Design

A new common-mode filter structure based on planar electromagnetic bandgap (EBG) technologies is designed, fabricated, and measured. It is based on a previously proposed geometry, implementing a sequence of two or more EBGs resonating at a filtering frequency; however, the new filter is placed on the top of the PCB as a standalone component, instead of being included within the PCB stack up. The filter can be easily removed and substituted by another one that is designed to filter a different frequency. The replacement design should maintain the same external size of the component as the original filter, which can be achieved by choosing the permittivity of the dielectric as well as the relationship among the EBG parameters appropriately. The electromagnetic behavior of the filter is simulated and a prototype structure is fabricated and measured. Results are compared to validate the design concept and procedure.

EBG-Based Common-Mode Stripline Filters: Experimental Investigation on Interlayer Crosstalk

This paper deals with the filters based on EBG cavities employed for reducing common-mode currents along differential stripline traces. The crosstalk among differential interconnects routed in close proximity to EBG-based filters, and next to filtered pairs, is accurately quantified. The comparison between the experimental and simulation frequency-domain results validate the proposed filters effectiveness and make the simulation model reliable for investigating the complex multichannel crosstalk problem. This paper focuses on the stripline environment, where crosstalk occurs among traces routed on adjacent layers, with the EBG cavity acting as a coupling path. Multichannel time-domain simulations complete the characterization of the filter, showing the limited effects of the filter on the intentional differential signal, and the beneficial impact on reducing the potentially radiating common-mode harmonics. The quantification of the common-mode spectrum shows that the filtered harmonics are reduced by 10-15 dB; thus, minimizing the corresponding electromagnetic interference. Design guidelines are defined for the filter layout according to the relative position of unfiltered differential traces, when constraints force them to be placed in close proximity to EBG cavities and filtered pairs. In particular, the best layout for unfiltered traces on adjacent layers is orthogonal with respect to the filtered pair, whereas the parallel routing should be carefully used taking into account the signal bandwidth on the victim pairs.

On finding the optimal number of decoupling capacitors by minimizing the equivalent inductance of the PCB PDN

PCB-PDN design remains a challenge with the reducing noise margins. One aspect of PDN design is finding the number of decoupling capacitors required for each power rail. As more capacitors are added, the mid frequency equivalent inductance in the impedance of the PCB-PDN converges to a minimum value for each placement pattern. This convergence is studied for different placement patterns to find the least number of capacitors required to satisfy a certain convergence criteria. A first principle method is used resonant cavity model for the analysis.

Modeling Electromagnetic Radiation at High-Density Pcb/connector Interfaces

Electromagnetic radiation for a commercial printed circuit board (PCB) connector is investigated in this paper. The simulation models of the connector are shown to be validated by comparing measured and simulated S-parameters. Analytical formulas are provided to calculate the total loss and the radiated power from a PCB/connector structure when material losses are known. The total power loss for the considered geometry is shown to be dominated by material loss rather than radiated power loss. Termination schemes and additional geometry details in the connector model are also studied for their effects on the radiated power.

Reduction of EMI Due to Common-Mode Currents Using a Surface-Mount EBG-Based Filter

Common-mode (CM) noise on differential signals can be suppressed by planar electromagnetic bandgap (EBG) technologies. In this study, two new CM filter structures were designed, fabricated, and measured. The filters are based on a previously proposed geometry, a “sandwich-type” EBG structure that resonates at the desired filter frequency; however, the new filters are placed on the top of the PCB as a surface-mount component, instead of being implemented within the PCB stackup. Stripline and microstrip versions of the surface-mount filter are considered. The filters can be easily removed and substituted with another one that is designed to filter a different frequency but maintains the same footprint and external dimensions. In addition, the surface-mount filter allows us to incorporate dc blocking capacitors into the microstrip version of the filter, thus providing two functions in one package. The total radiated power (TRP) of the implemented filter is investigated and discussed. RF absorbing material and traditional shielding are considered to reduce the TRP.

Electronic packaging of the IBM z13 processor drawer

IBM z13 processor drawer W. D. Becker H. Harrer A. Huber W. L. Brodsky R. Krabbenhoft M. A. Cracraft D. Kaller G. Edlund T. Strach The electronic packaging of the IBM z13i is the foundation for a processor drawer that provides a significant increase in processing power relative to the IBM zEnterpriseA EC12 (zEC12) system while managing power and cost to meet the z13 product objectives. The z13 system architecture differs from previous high-end z Systemsi designs due to the introduction of a drawer-based processor design, organic single-chip modules (SCMs) in place of the ceramic MCMs (multi-chip modules), and a cabled interconnect between drawers in place of the PCB (printed circuit board) backplane of the zEC12. These innovations are coupled with next-generation signaling interfaces, providing a significant increase in signal bandwidth. The next-generation voltage regulation and decoupling provides the efficient power delivery needed to build a new processor subsystem with 40% more processor cores than the zEC12. The memory bandwidth and capacity have more than tripled, and the input/output bandwidth of the processor chip doubled to provide excellent scalability at the processor socket, drawer, and system level. The electronic packaging has been designed to meet all of these challenges, and this paper presents the design and integration of the electronic packaging of the z13 system.

Analytical PDN voltage ripple calculation using simplified equivalent circuit model of PCB PDN

Printed circuit board (PCB) power distribution network (PDN) design performance depends on the peak voltage ripple caused by the integrated circuit (IC) switching currents. The input impedance seen by the IC looking into the PCB PDN can be calculated using a physics-based circuit model extracted from the cavity model approach. The input impedance is fitted to a simplified circuit model used to represent the PCB PDN. Using a switching current profile, the frequency domain noise voltage is found and transformed to the time domain ripple waveform which can then be used to evaluate the PDN design performance.

Standalone removable EBG-based common mode filter for high speed differential signaling

A new structure is proposed in this paper to realize a common mode filter based on the EBG technology. It is based on the geometry previously proposed as a sequence of two or more EBGs resonating at the filtering frequency; however the new filter is placed on top of the PCB as a standalone component, instead of being included within the PCB stackup. The filter can be easily removed and substituted by another one designed to filter a different frequency. The new frequency design should ensure the same external size of the component as the original filter which can be achieved by choosing the permittivity of the dielectric as well as the relationship among the EBG parameters appropriately. The electromagnetic behavior of the filter is studied based on the current path responsible for the excitation of the EBG resonance; the methodology for a correct design is developed proposing different design configurations.

Mitigating the threat of crosstalk and unwanted radiation when using electromagnetic bandgap structures to suppress common mode signal propagation in PCB differential interconnects

Common-mode noise in high-speed differential signaling results in significant signal integrity and EMI concerns. Past work has shown that common-mode filters based on electromagnetic bandgap (EBG) structures can be implemented using standard PCB technology and are effective in suppressing common mode transmission on differential interconnects. This common-mode energy, when filtered, can result in crosstalk or unintentional radiation. In the work described here, the radiation mechanisms in the electromagnetic bandgap structure are examined and a solution involving via stitching and via fences is proposed.