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
