Transcript Signal integrity of high speed digital PCB designs

SIGNAL INTEGRITY OF HIGH
SPEED DIGITAL PCB DESIGNS
EECS 713 Project
Instructor: Prof. Allen
Presented by: Chen Jia
Definition
 Signal integrity (SI): is a set of measures of
the quality of an electrical signal. We expect
the signal can response time series, electrical
level correspondingly.
 Was not always a case in earlier days.
Challenges for designers
 Concerns: why, what, when, and how
Why
 When
SI happens, the noise margin
requirement will not be satisfied – logic
errors, false switching, system collapses, etc.
 In high speed digital system, we are
expecting a string that contains bits H(1) and
L(0). A continuous voltage waveform.
Receivers sample the signal by generating the
rising and falling edge of the signal.
Settle down to non-ambiguous before receiver kicks in
A Failure in catching rising or falling edge, or
misreading an ambiguous logic state may result
in an incomplete data transmission or even
a failure of transmission.
We want to see this
Not this
When
Delay
 If the signal arrives its destination when it is
supposed to.
 Delay depends on the length of the
transmission line and dielectric constant. In
high speed digital system, the length of the
transmission lines has the greatest impact of
clock skew.
Clock skew: is the difference in the arrival time
between two sequentially-adjacent registers
What
 Parameters of PCB and components on it
 The arrangement of components layout and
high speed trace design
 Reflection/crosstalk/power/ground noise
 Electromagnetic Compatibility (EMC)
 Electromagnetic Interference (EMI)
How
Solution:
crosstalk, reflection
 For crosstalk:
 1. Reduce the coupling (a solid reference plane, both
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ground and power plane will do)
2. Change the timing
3. Improve receiver noise margins (as we stated
before)
4. Downsize the aggressor nets (prevent large
voltages from affecting small ones, not always the
case with digital logic)
5. 90 degree routing, avoid parallel layout (to
minimize the impact)
6. More…
Solutions
 For reflections:
 Happens when impedance changes while the
signal is transmitting.
 L> Tr/2Tpd
 Tpd: Transport Delay/unit length
 Impedance matching:
Matching
 1. Parallel: load impedance matching (close to
load side)
2. Series: source impedance matching (close
to source side, R + Rs ≥ RL)
Summary
Prototype
System
requirements
Constrain driven
layout
Schematic
component
placement
Meet SI
requirement?
Physical design
Production
Practical
measurements
Interconnection
components
selection
Reference
 http://www.csee.umbc.edu/csee/research/vlsi
/
 http://www.cc362.com/article/44852226.html
 http://www.mr-wu.cn/signal-integrityanalysis-for-high-speed-digital-pcb/
 http://www.sigcon.com/Pubs/news/6_01.htm
Thank you !