A 26 \mu W 8 bit 10 MS/s Asynchronous SAR ADC for Low Energy Radios

• Published in: IEEE journal of solid-state circuits 2011-07, Vol.46 (7), p.1585-1595
• Main Authors: Harpe, P. J. A., Zhou, C., Yu Bi, van der Meijs, N. P., Xiaoyan Wang, Philips, K., Dolmans, G., de Groot, H.
• Format: Article
• Language: English
• Subjects: ADC; analog-to-digital conversion; asynchronous; Capacitance; Capacitors; CMOS; Direct power generation; Dynamics; Layout; Low energy; Metals; MIM capacitors; Power consumption; Power demand; Radio; Sampling; successive approximation; Switches; Synthetic aperture radar
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2011.2143870

This paper presents an asynchronous SAR ADC for flexible, low energy radios. To achieve excellent power efficiency for a relatively moderate resolution, various techniques are introduced to reduce the power consumption: custom-designed 0.5 fF unit capacitors minimize the analog power consumption while asynchronous dynamic logic minimizes the digital power consumption. The variability of the custom-designed capacitors is estimated by a specialized CAD tool and verified by chip measurements. An implemented 8-bit prototype in a 90 nm CMOS technology occupies 228 μm × 240 μm including decoupling capacitors, and achieves an ENOB of 7.77 bit at a sampling frequency of 10.24 MS/s. The power consumption equals 26.3 μW from a 1 V supply, thus resulting in an energy efficiency of 12 fJ/conversion-step. Moreover, the fully dynamic design, which is optimized for low-leakage, leads to a standby power consumption of 6 nW. In that way, the energy efficiency of this converter can be maintained down to very low sampling rates.