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AUGUST 2019 I DESIGN007 MAGAZINE 53 place the decoupling capacitors on the same side of the board as the BGA for high layer-count stackups • Capacitor mounting loop area can be re- duced by placing the vias closer to the lands • Vias should be directly connected to the plane rather than by thermal reliefs, which adds to the inductance • Current flow is a round trip, and the im- portant issue is delay, not length • Return path discontinuities can also create large loop areas that increase series induc- tance • RPDs produce impedance discontinuities due to the local return inductance and ca- pacitive changes • If the return path of a common mode cur- rent is far from the signal path, then the common mode current will radiate Further Reading • Olney, B. "Beyond Design: Crosstalk Mar- gins," Design007 Magazine, July 2018. • Olney, B. "Beyond Design: Power Distribu- tion Network Planning," The PCB Maga- zine, May 2012. • Olney, B. "Beyond Design: PDN Planning and Capacitor Selection, Part 1," The PCB Design Magazine, December 2013. • Olney, B. "Beyond Design: PDN Planning and Capacitor Selection, Part 2," The PCB Design Magazine, January 2014. • Olney, B. "Beyond Design: Return Path Dis- continuities," The PCB Design Magazine, April 2017. • Olney, B. "Beyond Design: Common Symp- toms of Common-Mode Radiation," De- sign007 Magazine, May 2018. • Morrison, R. Fast Circuit Boards: Energy Management, John Wiley & Sons, 2018. • Cadence PCB Solutions. "How Parasitic Ca- pacitance and Inductance Affect Your Sig- nals," Cadence Design Systems Inc., May 2, 2019. • Bogatin, E. Signal and Power Integrity: Sim- plified, Prentice Hall, 2008. • Johnson, H. W., & Graham, M. High-Speed Digital Design: A Handbook of Black Magic, Prentice Hall, 1993. DESIGN007 Barry Olney is managing director of In- Circuit Design Pty Ltd. (iCD), Australia, a PCB design service bureau that spe- cializes in board-level simulation. The company developed the iCD Design Integrity software incorporating the iCD Stackup, PDN, and CPW Planner. The software can be downloaded To read past columns or contact Olney, click here. The startup kiutra GmbH is the first company in the world to have succeeded in developing a permanent magnet- ic cooling system to reach temperatures close to absolute zero. Such temperatures are, for example, required for the operation of quantum computers. The system was set up by a team of researchers from the Physics Department at the Technical University of Munich (TUM). TUM researchers Alexander Regnat, Jan Spallek, Tomek Schulz, and Professor Christian Pfleiderer are seeking to meet that demand. All four are currently working on their prototype at the TUM Physics Department. According to Al - exander Regnat, there is already the prospect of taking on more staff and setting up separate headquarters. The team of scientist came up with the idea during their work at the TUM. Again and again, they were faced with the limits of conventional methods for reaching such low tem- peratures. Therefore, the group developed its own technol- ogy to ensure permanent cooling and founded kiutra GmbH in the summer of 2018. Concepts for permanent magnetic cooling have been around for many years. "However, technical implementation is extremely challenging, and this has previously prevented the development of a product for widespread use," explains Schulz. "We are the world's first commercial supplier of a cooling system that can magnetically achieve temperatures close to absolute zero (near -273°C) on a permanent basis," says Regnat. (Source: Science and Technology Research News) Cooling for Quantum Electronics

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