44 The PCB Design Magazine • February 2016
• One of the most important ways to deter-
mine the quality of a digital transmission
system is to measure its bit error ratio
(BER).
• An eye diagram is a common indicator of
the quality of signals in high-speed digital
transmissions.
• In high-speed multilayer PCBs, we need
to select the material with the lowest di-
electric constant (aka Dk) and the lowest
dielectric loss (Df) in order to achieve the
maximum bandwidth.
• The higher the operating frequency and
the lower the loss, the easier it is to get
wider bandwidths.
PCBDESIGN
References
1. Barry Olney, Beyond Design: Matched
Length Does not Equal Matched Delay, Trans-
mission Lines
2. Robert Dahlgren: Noise in Fiber Optic
Communications Links
3. Lau, Zhang, Lee: Opto-electronic Inter-
connect in Organic Substrate
4. Bruce Archambeault: PCB Design for Real-
World EMI Control
5. Howard Johnson: High-speed Signal Prop-
agation
6. www.physics.stackexchange.com
7. Alan Finkel: Cosmos, Issue 61, "Silicon is
King"
8. The ICD Stackup and PDN Planner: www.
icd.com.au
Barry Olney is managing director
of In-Circuit Design Pty Ltd (ICD),
Australia. This PCB design service
bureau specializes in board-level
simulation, and has developed the
ICD Stackup Planner and ICD PDn
Planner software. To read past col-
umns, or to contact olney, click here.
In an advance reported in na-
ture Chemistry, scientists at the
University of Liverpool have shown
that it is possible to design and
construct interfaces between ma-
terials with different structures by
making a bridge between them.
It is usually possible to make
well-controlled interfaces when
two materials have similar crystal structures, yet
the ability to combine materials with different
crystal structures has lacked the accurate design
rules that increasingly exists in other areas of ma-
terials chemistry.
The design and formation of an atomic-scale
bridge between different materials will lead to new
and improved physical properties, opening the
path to new information technology and energy
science applications amongst a myriad of science
and engineering possibilities. For example, atoms
could move faster at the interface between the
materials, enabling better batteries and fuel cells.
Liverpool Materials Chemist Professor Matthew
Rosseinsky said, "When we try to
fit materials together at the atomic
scale, we are used to using the sizes
of the atoms to decide which com-
binations of materials will "work"
i.e. will produce a continuous well-
ordered interface.
"The project team added in con-
sideration of the chemical bonding
around the atoms involved, as well as their sizes,
as a key design step. This allowed the selection of
two materials with different crystal structures yet
with sufficient chemical flexibility to grow in a
completely ordered manner throughout the inter-
face between them.
"This was achieved by the formation of a unique
ordered structure at the interface which did not
correspond to either material but contained fea-
tures of both of them, an atomic-scale bridge."
It is possible to construct a flexible block, which
will fit with both materials, and bridge the gap be-
tween them, like the blue blocks bridge the gap
between the red and green ones.
Scientists Bridge Different Materials by Design
faster than a speeding Bullet
