Robust and energy-efficient asynchronous dynamic pipelines for ultra-low-voltage operation using adaptive keeper control

Asynchronous dynamic pipelines are increasingly being used, including in recent commercial design flows, since they simultaneously provide high-performance, clock-free operation and delay-insensitive communication. While they also show promise for energy-efficient ultra-low-voltage circuits, with always-on keepers, these circuits exhibit severe robustness issues. In this paper, an adaptive keeper solution is introduced, to eliminate write contention issues. Arbitrary unknown data rates and congestion must be safely handled, without a reference clock, hence conventional solutions for synchronous design cannot be applied. The proposed method, demonstrated in two widely-used pipelines (PS0, PCHB), directly addresses the asynchronous contention issue by dynamic monitoring of neighboring traffic at each pipeline stage. Simulations of a pipelined ripple-carry adder show correct operation at 0.3 V with energy improvements of up to 4.4× compared to a non-adaptive design. In addition, the approach also improves pipeline throughput by 24.4% and 17.4% at 0.6 V and nominal 1.0 V, respectively.