Negative Design Margin Realization through Deep Path Activity Detection Combined with Dynamic Voltage Scaling in a 55 nm Near-Threshold 32-Bit Microcontroller

Abstract

This paper presents an innovative approach for predicting timing errors tailored to near-/sub-threshold operations, addressing the energy-efficient requirements of digital circuits in applications, such as IoT devices and wearables. The method involves assessing deep path activity within an adjustable window prior to the root clock’s rising edge. By dynamically adapting the prediction window and supply voltage based on error detection outcomes, the approach effectively mitigates false predictions—an essential concern in low-voltage prediction techniques. The efficacy of this strategy is demonstrated through its implementation in a near-/sub-threshold 32-bit microprocessor system. The approach incurs only a modest 6.84% area overhead attributed to well-engineered lightweight design methodologies. Furthermore, with the integration of clock gating, the system functions seamlessly across a voltage range of 0.4 V–1.2 V (5–100 MHz), effectively catering to adaptive energy efficiency. Empirical results highlight the potential of the proposed strategy, achieving a significant 46.95% energy reduction at the Minimum Energy Point (MEP, 15 MHz) compared to signoff margins. Additionally, a 19.75% energy decrease is observed compared to the zero-margin operation, demonstrating successful realization of negative margins.

Margin Elimination in a 55 nm Near-Threshold Microcontroller with Adaptive Prediction Capability and Voltage Scaling

“…In order to overcome the drawbacks in the existing EDaC and EP techniques, this work aims to combine the benefits of predicting errors before the clock edge (i.e., no hold constraints, high error-aware capacity, and one cycle correction) and detecting errors after the clock edge (i.e., no margins) into a novel EP concept. The concept, initially introduced in our prior work [13], involves the incorporation of transition detection (TD) cells deeply inserted in the critical paths. These cells are designed to convert critical data transitions within an adjustable prediction window (PW) just prior to the root clock's rising edge into prediction timing error signals.…”