Signal Integrity Friday June 25 2011 Vikram Jandhyala vj ... · Serialization-Deserialization ....
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Signal Integrity V. Jandhyala
Signal Integrity
Friday June 25 2011 Vikram Jandhyala
Professor, UWEE Founder, Physware, Inc.
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Signal Integrity V. Jandhyala
What is signal integrity ? • The challenges and problems that arise in high-
speed products due to propagation path effects
• Especially in interconnects – On-chip – Chip-to-Chip – Package – Board – Backplane
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Signal Integrity V. Jandhyala
Transmission Line Example
• What do you expect to see at Vout ?
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Signal Integrity V. Jandhyala
Delay • “Time of Flight”: Related to velocity of light
and distance.
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Signal Integrity V. Jandhyala
Loss
• (Typically) Higher frequency components are “attenuated”
• Loss caused by – Metal – Material (Dielectric) – Radiation
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Signal Integrity V. Jandhyala
EMI Radiation
Courtesy: Physware
Transistor switching on chip causing system-level radiation hotspots
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Signal Integrity V. Jandhyala
Dispersion
• Different frequencies travel at different velocities
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Signal Integrity V. Jandhyala
Mismatch
• Driver impedance • Line impedance • Receiver impedance
• Any mismatch causes additional effects
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Signal Integrity V. Jandhyala
Mismatch
• Normally seen at 100 MHz or higher clock rates
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Signal Integrity V. Jandhyala
Serialization-Deserialization
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Signal Integrity V. Jandhyala
Serdes:Differential signaling
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Signal Integrity V. Jandhyala
Applications of high-speed links
• Processor to memory • Peripherals and hard drives • USB • HDMI and Video • Flash • Ethernet backplane • Infiniband-server backplane
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Signal Integrity V. Jandhyala
Differential signals and eye diagrams
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Signal Integrity V. Jandhyala
Eye diagrams
• Eye is produced by multiple passes of differential (equal and opposite signals)
• Jitter: timing randomness and amplitude randomness arising due to – Asymmetries in a differential system – Thermal and noise effects – Crosstalk and inter-symbol interference
• LlNK to an eye diagram animation on YouTube
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Signal Integrity V. Jandhyala
From an SI angle, why use Serdes?
• Why would you switch from signal-ended, low-speed, multiple parallel lines to a differential, high-speed, serial line. Any issues to expect ?
• Benefits: Less crosstalk, less noise, potentially less real estate
• Challenges: Higher-speed signals imply high-frequency SI effects: dispersion, radiation – Some of these may be mitigated due to differential
design
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Signal Integrity V. Jandhyala
Crosstalk
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Signal Integrity V. Jandhyala
Signal paths
Courtesy: Physware
Potential for large crosstalk
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Signal Integrity V. Jandhyala
Models
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Signal Integrity V. Jandhyala
Models
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Signal Integrity V. Jandhyala
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Signal Integrity V. Jandhyala
S-parameters
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Signal Integrity V. Jandhyala
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Signal Integrity V. Jandhyala
Computing S-parameters • From lumped-circuit models
– Z to S – Least accurate and easiest
• From transmission line models – 1D Wave equations – Intermediate complexity and accuracy
• From mesh-based solution to Maxwell’s equations – 3D Wave equations – Most complex and high accuracy
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Signal Integrity V. Jandhyala
S-parameter matrix
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Signal Integrity V. Jandhyala
S-parameters Reflection
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Signal Integrity V. Jandhyala
S-parameters Transmission
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Signal Integrity V. Jandhyala
Memory
Courtesy: Physware
No well-defined ground-plane: Will reduce transmission
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Signal Integrity V. Jandhyala
Return current spreading
Courtesy: Physware
Deviation from ideal differential design: reduces transmission
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Signal Integrity V. Jandhyala
Differential signaling
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Signal Integrity V. Jandhyala
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Signal Integrity V. Jandhyala
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Signal Integrity V. Jandhyala
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Signal Integrity V. Jandhyala
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Signal Integrity V. Jandhyala
Negatives
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Signal Integrity V. Jandhyala
Sources • EE 571 Notes Vikram Jandhyala • Bogatin: signal integrity, Prentice Hall • Young: Digital signal integrity, Prentice Hall • www.physware.com • http://www.altera.com/products/ip/dsp/images/
lvds-tx-rx-ip-blockdiagram.gif • http://i.cmpnet.com/eet/news/03/january/
SS1254_FAIRCHILD.gif • http://www.latticesemi.com/images/img12682.jpg • http://www.youtube.com/watch?v=my7CI84le5g