Injection Locked Clocking with Ring Oscillators Rachel Nancollas and Suchit Bhattarai

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

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

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.

Current Starved Ring Oscillators

System Overview Conventional Clocking Network Injection Locked Ring Oscillator Clocking Network

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

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

Simulation Results master ILRO conventional

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

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