Journal
IEEE JOURNAL OF SOLID-STATE CIRCUITS
Volume 55, Issue 2, Pages 414-425Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JSSC.2019.2957193
Keywords
Chopper amplifier; current reuse; electrocardiogram (ECG); inverter-based operational transconductance amplifier (OTA); low power; noise efficiency
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Funding
- UCSD Center for Wireless Communications
- DURIP Award from the Office of Naval Research [N00014-18-1-2350]
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An ultra-low power electrocardiogram (ECG) recording front-end intended for implantable sensors is presented. The noise-limited, high power first stage of a two-stage amplifier utilizes stacking of operational transconductance amplifiers (OTAs) for noise and power efficiency improvements. The proposed technique involves upmodulated/chopped signals being applied to ac-coupled, stacked inverter-based OTAs that inherently sum the individual transconductances while reusing the same current, thereby enhancing the noise efficiency. Two prototype designs were fabricated in a 180-nm CMOS process. The three-stack version consumes 13.2 nW and occupies 0.18 mm(2), whereas the five-stack implementation consumes 18.7 nW and occupies 0.24 mm(2). State-of-the-art NEF and PEF metrics of less than unity, 0.86 and 0.99, respectively, are reported for the five-stack version. These correspond to 3 $\times $ improvement in terms of energy efficiency compared to prior ultra-low power, sub-100-nW amplifiers.
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