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66 The PCB Design Magazine • June 2016 on differential signals, that can easily be avoid- ed. Solutions for breaking a pair, termination, change of reference planes, trace skew and DC blocking layout techniques are described in de- tail. Finally, one of the most important aspects of HSDD is revealed: clock distribution. All you ever wanted to know about effectively rout- ing clocks, loaded delay, the forward crosstalk (FEXT) of serpentine traces, daisy-chain routing of multiple loads and the effects of jitter on clock eyes. Dr. Johnson's collection is a must-see for all digital design engineers and PCB designers who need to understand electromagnetic theo- ry, appreciate how coupling occurs and why en- ergy moves to unintended, sensitive parts of the circuits. And, more importantly, how to prevent electromagnetic coupling. I read that when Albert Einstein was teach- ing at Princeton, he prepared an examination paper and handed it to his assistant. The assis- tant queried, "Albert, isn't this the same exam you gave this class last year?" Einstein replied, "Yes it is. The questions are the same, but the answers have changed!" Digital designers need to keep up with the fast changing pace of technology. For all the lat- est solutions, to complex Signal Integrity issues, I recommend the High-Speed Digital Design Collection. PCBDESIGN References 1. Dr. Howard Johnson, Signal Consulting: High-Speed Digital Design Collection 2. Howard Johnson, Martin Graham: High- Speed Digital Design – A Handbook of Black Magic 3. Howard Johnson, Martin Graham: High- Speed Signal Propagation – Advanced Black Magic Barry Olney is managing director of In-Circuit Design Pty Ltd (ICD) Australia. The company is a PCB design service bureau that special- izes in board-level simulation. ICD has developed the ICD Stackup Planner and ICD PDN Planner soft- ware, which is available here. MASTERING "BLACK MAGIC" WITH HOWARD JOHNSON'S SEMINARS Using the Continuous Elec- tron Beam Accelerator Facility (CEBAF) at the Department of Energy's Jefferson Lab, a team of researchers has, for the first time, demonstrated a new tech- nique for producing polarized positrons. Jefferson Lab Injector Scien- tist Joe Grames says the idea for the method grew out of the many advances that have been made in understanding and controlling the elec- tron beams used for research in CEBAF. "We have a lot of experience here at Jefferson Lab in operating a world-leading electron acceler- ator," Grames said. "We are constantly improving the electron beam for the experiments, pushing the limits of what we can get the electrons to do." Grames and his colleagues would like to take that finesse a step further and transform CEBAF's well-con- trolled polarized electron beams into well-controlled beams of polarized positrons to offer re- searchers at Jefferson Lab an ad- ditional probe of nuclear mat- ter. They named the endeavor the Polarized Electrons for Po- larized Positrons experiment, or PEPPo. Throughout the process, the polarization of the original electron beam is passed along. The researchers use a magnet to siphon the positrons away from the other particles and direct them into a detector system that measures their energy and polarization. "We showed that there's a very efficient trans- fer of polarization from electrons to the positrons," said Grames. Spinning Electrons Yield Positrons for Research

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