Transcript Injection Locked Clocking with Ring Oscillators

Injection
Locked Clocking
with Ring
Oscillators
Rachel Nancollas and Suchit Bhattarai
Motivation:
Problems with Clocking
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Energy
Skew
Source:
Lin Zhang, PhD thesis
Is Injection Locked Clocking (ILC) the solution?
Injection Locked Clocking
source:
Lin Zhang, et al.
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Weak injecting signal locks local oscillator to global
frequency
This means the previous buffers can be smaller
Current Implementations
source: Lin Zhang, et al.
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Current oscillator designs
o LC Tanks
o Complex digital feedback (MDLLs)
Proposal: ILC with ring oscillators
source: H. Ng, et al.
Current Starved Ring
Oscillators
System Overview
Conventional Clocking Network
Injection Locked Ring Oscillator Clocking Network
Analytical Optimization
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Optimize EDP
Variables
o Stage 1: number of stages (N), fanout (fn)
o Stage 2: number of stages (M), fanout (fm)
o Injection Buffer Size (C_inj)
Process:
o Optimize EDP for stage 1 and 2: N, M, fn, fm as a
function of C_inj
o Find total EDP: choose C_inj to get min EDP
Optimization Results
• Energy is similar
• ILRO has higher delay
optimization
pushes fanout to
later stages
o pays energy of
slave oscillator
Conclusion: ILRO
doesn't look good
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Simulation Results
master
ILRO
conventional
Interconnect Variations
• Varied interconnect by
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10%
o Conventional ~ 4%
delay variation
o ILRO ~ 2% delay
variation
Result: ILRO is more
tolerant to interconnect
variation
Conclusions
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We developed a model for optimal sizing of ILRO clock
trees
ILROs are less energy efficient and more prone to skew
than conventional clock networks
ILROs may be more tolerant to interconnect variations
Result for ILC: still no small area oscillators
appropriate for digital systems