1. Injection Locked Clocking with Ring Oscillators
Rachel Nancollas and Suchit Bhattarai

2. Motivation: Problems with Clocking
Energy
Skew
Source:
Lin Zhang, PhD thesis
Is Injection Locked Clocking (ILC) the solution?

3. Injection Locked Clocking
source:
Lin Zhang, et al.
Weak injecting signal locks local oscillator to global frequency
This means the previous buffers can be smaller

4. Current Implementations
source: Lin Zhang, et al.
Current oscillator designs
LC Tanks
Complex digital feedback (MDLLs)
Proposal: ILC with ring oscillators
source: H. Ng, et al.

5. Current Starved Ring Oscillators

6. System Overview Conventional Clocking Network
Injection Locked Ring Oscillator Clocking Network

7. Analytical Optimization
Optimize EDP
Variables
Stage 1: number of stages (N), fanout (fn)
Stage 2: number of stages (M), fanout (fm)
Injection Buffer Size (C_inj)
Process:
Optimize EDP for stage 1 and 2: N, M, fn, fm as a function of C_inj
Find total EDP: choose C_inj to get min EDP

8. Optimization Results Energy is similar ILRO has higher delay
optimization pushes fanout to later stages
pays energy of slave oscillator
Conclusion: ILRO doesn't look good

9. Simulation Results
master
ILRO
conventional

10. Interconnect Variations
Varied interconnect by 10%
Conventional ~ 4% delay variation
ILRO ~ 2% delay variation
Result: ILRO is more tolerant to interconnect variation

11. Conclusions
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