To minimize energy consumption of a digital circuit, logic can be operated at sub- or near-threshold voltage. Operation at this region is challenging due to device and environment variations, and resulting performance may not be adequate to all applications. This article presents two variants of a 32-bit RISC CPU targeted for near-threshold voltage. Both CPUs are placed on the same die and manufactured in 28 nm CMOS process. They employ timing-error prevention with clock stretching to enable operation with minimal safety margins while maximizing performance and energy efficiency at a given operating point. Measurements show minimum energy of 3.15 pJ/cyc at 400 mV, which corresponds to 39% energy saving compared to operation based on static signoff timing. © 2015 by the authors; licensee MDPI, Basel, Switzerland.
- clock stretching
- digital CMOS
- timing-error prevention (TEP)
- ultra-low power (ULP)
Hiiekari, M., Teittinen, J., Koskinen, L., Turnquist, M. J., Mäkipää, J., Rantala, A., Sopanen, M., & Kaltiokallio, M. (2015). A robust ultra-low voltage CPU utilizing timing-error prevention. Journal of Low Power Electronics and Applications, 5(2), 57-68. https://doi.org/10.3390/jlpea5020057