Mixed Signal Coupling in Integrated Circuits

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Grounding Principles in Mixed-Signal
Board Docent Li-Rong Zheng Prof. Hannu
Tenhunen Laboratory of Electronics and Computer
Systems Royal Institute of Technology
(KTH) SE-164 40 Kista, Sweden (lrzheng_at_imit.kth.se
)
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Outline

• Simultaneous switching noise (SSN)
• Non-ideal return path
• Ground-referenced and power referenced signals
• Grounding principles

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Simultaneous switching noise (SSN)
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Simultaneous switching noise Component Level
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Simultaneous Switching Noise Component and Board
level
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Ground noise generation mechanism
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CMOS output driver
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Power Supply Noise and Signal Delay
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Non-Ideal Return Path
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Return Path of Signals
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Signal Traversing a Ground gap
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Modeling a signal traversing a gap
(in nH)
D in cm
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Non-ideal Return Path
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Signal that Change Reference Planes
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Ground-Referenced and Power Referenced Signals
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Ground Referenceand/or Power reference
Dual referenced signal reduces the current
through decoupling capacitor
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Ground Reference or Power Reference
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Ground Reference or Power Reference
6-9
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Grounding Principles for Mixed-Signal Systems
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Noise coupling through common impedance
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Common earth-return current coupling
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Single point vs. multipoint ground system
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Single point ground systems
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Hybrid ground systems
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Ground loop
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Functional ground layout
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AC vs. DC ground loops
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Inductance on ground loops (split-plane ground)

• Ground return cannot image to signal flow path
  and will cause an extra inductance.
• This inductance will cause switching noise
  voltage on ground (LdI/dt).
• If other pins share the same ground, crosstalk is
  also introduced.
• Common mode ground noise will result to common
  mode emission in case of drivers for cables/wires
  are connected to the same ground
• Resulting current loop can generate differential
  mode emission

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Inductance on ground loops (daugther cards)
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Ground loop elimination techniques
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I/O decoupling and shielding
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I/O decoupling and shielding
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Component placement on interconnect substrate
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Quiet I/O ground
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Reduction of loop areas
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Use of image planes to reduce radiated emission
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Grounding concepts