A 250-lW, 18-nV/rtHz current-feedback chopper instrumentation ampliﬁer in 180-nm cmos for high-performance bio-potential sensing applications Hyun-Sik Lee 1 • Van Nhan Nguyen 1 • Xuan Lap Pham 1 • Jong-Wook Lee 1 • Hun-Kuk Park 2 Received: 5 April 2016 / Revised: 14 June 2016 / Accepted: 29 August 2016 Ó Springer Science+Business Media New York 2016 Abstract This paper presents a low-power, high-perfor- mance current-feedback instrumentation ampliﬁer (CFIA) for portable bio-potential sensing applications. Noise anal- ysis is performed to assign an optimized current for the input stage of the ampliﬁer. Analysis on selecting nested chopping frequencies is performed, further reducing 1/f noise and the residual offset. Enhanced power efﬁciency is achieved by sharing cascode branches and using a Class-AB output stage. Through these methods, a good balance between noise per- formance and other parameters such as output ripples and power consumption of the ripple reduction feedback loop (RRFL) is achieved. The ampliﬁer is developed using a 1-poly 6-metal 0.18 lm CMOS process. Three gain stages with a gain-boosting input stage provide a low-frequency, open-loop gain [ 250 dB. When conﬁgured to a closed-loop gain of 60 dB, the ampliﬁer achieves a noise voltage density of 18 nV= ﬃﬃﬃﬃﬃ Hz p and a 1/f noise corner of 3 Hz. With a current of 75 lA and a supply voltage of 3.3 V, a CMRR of 110 dB and a PSRR of 120 dB are achieved, with an average input offset of about 6.5 lV. The ampliﬁer achieves a state-of-art noise efﬁciency factor of 4.2. Practical application of the CFIA is demonstrated with an in vivo electrocardiogram detection. Keywords Instrumentation ampliﬁer Á Current-feedback Á Power efﬁciency Á Bio-potential sensing Á Chopping Á 1/f noise 1 Introduction Recently, there has been considerable interest in portable, wearable, and personal health monitoring devices [1, 2]. These devices perform real-time monitoring of various everyday human activities. Based on analysis of an accu- mulated database, the devices can detect abnormal health conditions for realizing preventive healthcare. With regard to bio-potential monitoring applications, detector sensors and their interfaces that provide high-quality signals are of great importance. The higher the signal quality, the more reliable the health information can be derived. For bio- potential detecting systems, an instrumentation ampliﬁer is a critical building block. Bio-potential signals range from several lV to mV at frequencies less than about 1 kHz. For example, the frequency range of electrocardiogram (ECG) signal is from 0.1 to 150 Hz and its amplitude is a few mV [3]. In this frequency range, ﬂicker noise and electrode offset dominate the frequency spectrum. To obtain high- quality signals, the instrumentation ampliﬁer should pro- vide sufﬁcient gain while suppressing unwanted offset and ﬂicker noise. To eliminate the effects of ﬂicker noise, chopping is a preferred approach for a high-performance instrumentation ampliﬁer; compared to auto-zeroing, which is based on signal sampling, noise-folding effects do not occur with chopping. Voltage-feedback has traditionally been used to realize instrumentation ampliﬁers. Although they show good lin- earity, three low-noise opamps are required to realize a voltage-feedback instrumentation ampliﬁer (VFIA). & Jong-Wook Lee jwlee@khu.ac.kr Hun-Kuk Park sigmoidus@khu.ac.kr 1 School of Electronics and Information, Kyung Hee University, Yongin, Gyeonggi 17104, Korea 2 College of Medicine, Kyung Hee University, Seoul 022447, Korea 123 Analog Integr Circ Sig Process DOI 10.1007/s10470-016-0853-7