Phase Coding for Global OnChip Interconnects

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Phase Coding for Global On-Chip Interconnects

• Kai Zhou
• Advisor Prof. Burleson
• ECE Dept., UMass
• April, 2002

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Outline

• Motivation
• Introduction
• Design Issues
• Project
• Conclusions

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MotivationIssues in Global Signalling

• Repeater insertion to deal with performance
  degradation due to global interconnects
• Effective when interconnect resistance is
  relatively small
• With technology scaling, more repeaters are
  needed
• Increased repeaters result in more power
  consumption
• Techniques for high speed global signalling and
  less power consumption are required

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Some Techniques for Global Interconnects

• Current sensing
• Decreasing the number of interconnects
• Coding
• Multi-level signalling
• Phase coding

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Basic Principles of Phase Coding

• Pulse Width Modulation (PWM) in communication
  theory
• Pulse width reflects analog value
• Digital signal lines encoded using the PWM scheme
• Power saving
• High bandwidth

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Three Pulse Coding Schemes

• Pulse Width Modulation (PWM)
• Phase Coding (PC)
• Phase Coded Pulse Width Modulation (PCPWM)

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Three Pulse Coding Schemes(cont.)
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Another coding technique
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Encoding for PCPWM

• Each bit pattern will be characterized by a pulse
  
• Requirement for the number of partitions
• C(M,2) gt 2N
• M -- of partitions in a clock cycle
• N -- of bits

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Structure of Transmitter
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Phase Decoder

• Generate a pulse according to input clocks

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Structure of Receiver
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Design Issues

• Requirement of minimum width of the pulse
  information transferred should be recovered at
  receiving end
• Getting clock with the same delay as data
• Crosstalk noise and inductive noise
• Impacts of process variation
• Line length

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Variation of Transmitted Signals
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Project

• Do noise analysis of interconnects
• Study the impacts of process variations
• Get the data needed to further design of phase
  coding

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Conclusions

• Phase coding technique can result in possible
  bandwidth improvement and lower power consumption
• PCPWM enables an efficient coding, but has
  complex transmitter and receiver
• Noise might limit the number of signals that can
  be encoded

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References

• Mandeep Singh, Phase Coding for Global On-chip
  Interconnects, ECE Dept., Umass
• Stefanos Sidiropoulos, Chih-Kong Ken Yang, Mark
  Horowitz, Design of High Performance
  Microprocessor Circuits, Chapter 19, pp.397-405