{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,10]],"date-time":"2026-06-10T10:58:33Z","timestamp":1781089113024,"version":"3.54.1"},"reference-count":19,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2020,4,6]],"date-time":"2020-04-06T00:00:00Z","timestamp":1586131200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003725","name":"National Research Foundation of Korea","doi-asserted-by":"publisher","award":["NRF-2018R1A2A2A05018621"],"award-info":[{"award-number":["NRF-2018R1A2A2A05018621"]}],"id":[{"id":"10.13039\/501100003725","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>To realize an ultra-low-power and low-noise instrumentation amplifier (IA) for neural and biopotential signal sensing, we investigate two design techniques. The first technique uses a noise-efficient DC servo loop (DSL), which has been shown to be a high noise contributor. The proposed approach offers several advantages: (i) both the electrode offset and the input offset are rejected, (ii) a large capacitor is not needed in the DSL, (iii) by removing the charge dividing effect, the input-referred noise (IRN) is reduced, (iv) the noise from the DSL is further reduced by the gain of the first stage and by the transconductance ratio, and (v) the proposed DSL allows interfacing with a squeezed-inverter (SQI) stage. The proposed technique reduces the noise from the DSL to 12.5% of the overall noise. The second technique is to optimize noise performance using an SQI stage. Because the SQI stage is biased at a saturation limit of 2VDSAT, the bias current can be increased to reduce noise while maintaining low power consumption. The challenge of handling the mismatch in the SQI stage is addressed using a shared common-mode feedback (CMFB) loop, which achieves a common-mode rejection ratio (CMRR) of 105 dB. Using the proposed technique, a capacitively-coupled chopper instrumentation amplifier (CCIA) was fabricated using a 0.18-\u00b5m CMOS process. The measured result of the CCIA shows a relatively low noise density of 88 nV\/rtHz and an integrated noise of 1.5 \u00b5Vrms. These results correspond to a favorable noise efficiency factor (NEF) of 5.9 and a power efficiency factor (PEF) of 11.4.<\/jats:p>","DOI":"10.3390\/s20072059","type":"journal-article","created":{"date-parts":[[2020,4,7]],"date-time":"2020-04-07T03:58:39Z","timestamp":1586231919000},"page":"2059","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["A 0.6-\u00b5W Chopper Amplifier Using a Noise-Efficient DC Servo Loop and Squeezed-Inverter Stage for Power-Efficient Biopotential Sensing"],"prefix":"10.3390","volume":"20","author":[{"given":"Xuan Thanh","family":"Pham","sequence":"first","affiliation":[{"name":"School of Electronics and Information, Information and Communication System-on-chip (SoC) Research Center, Kyung Hee University, Yongin 17104, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ngoc Tan","family":"Nguyen","sequence":"additional","affiliation":[{"name":"School of Electronics and Information, Information and Communication System-on-chip (SoC) Research Center, Kyung Hee University, Yongin 17104, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Van Truong","family":"Nguyen","sequence":"additional","affiliation":[{"name":"School of Electronics and Information, Information and Communication System-on-chip (SoC) Research Center, Kyung Hee University, Yongin 17104, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9160-2183","authenticated-orcid":false,"given":"Jong-Wook","family":"Lee","sequence":"additional","affiliation":[{"name":"School of Electronics and Information, Information and Communication System-on-chip (SoC) Research Center, Kyung Hee University, Yongin 17104, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,4,6]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Jiang, X., Bian, G.-B., and Tian, Z. (2019). Removal of artifacts from EEG signals: A review. Sensors, 19.","DOI":"10.3390\/s19050987"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"12847","DOI":"10.3390\/s140712847","article-title":"Dry EEG electrode","volume":"14","year":"2014","journal-title":"Sensors"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"2934","DOI":"10.1109\/JSSC.2007.908664","article-title":"A 2 \u03bcW 100 nV\/\u221aHz chopper-stabilized instrumentation amplifier for chronic measurement of neural field potentials","volume":"42","author":"Denison","year":"2007","journal-title":"IEEE J. Solid State Circuits"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1534","DOI":"10.1109\/JSSC.2011.2143610","article-title":"A 1.8 \u03bcW 60 nV\/\u221aHz capacitively-coupled chopper instrumentation amplifier in 65 nm CMOS for wireless sensor nodes","volume":"46","author":"Fan","year":"2011","journal-title":"IEEE J. Solid State Circuits"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"555","DOI":"10.1109\/TBCAS.2011.2170985","article-title":"A 160 \u03bcW 8-channel active electrode system for EEG monitoring","volume":"5","author":"Xu","year":"2011","journal-title":"IEEE Trans. Biomed. Circuits Syst."},{"key":"ref_6","first-page":"523","article-title":"0.5 V 1.3 \u00b5V analog front-end CMOS circuit","volume":"63","author":"Zhu","year":"2016","journal-title":"IEEE Trans. Circuits Syst. II Express Briefs"},{"key":"ref_7","first-page":"1392","article-title":"Chopper capacitively coupled instrumentation amplifier capable of handling large electrode offset for biopotential recordings","volume":"64","author":"Zheng","year":"2017","journal-title":"IEEE Trans. Circuits Syst. II Express Briefs"},{"key":"ref_8","first-page":"351","article-title":"A 2-\u03bcW 45-nV\/\u221aHz readout front end with multiple-chopping active-high-pass ripple reduction loop and pseudo feedback DC servo loop","volume":"63","author":"Wu","year":"2016","journal-title":"IEEE Trans. Circuits Syst. II Express Briefs"},{"key":"ref_9","unstructured":"Huang, G., Yin, T., Wu, Q., Zhu, Y., and Yang, H.A. (2015, January 24\u201327). 1.3 \u03bcW 0.7 \u03bcVRMS chopper current-reuse instrumentation amplifier for EEG applications. Proceedings of the 2015 IEEE International Symposium on Circuits and Systems (ISCAS), Lisbon, Portugal."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"3032","DOI":"10.1109\/JSSC.2017.2746778","article-title":"A noise-efficient 36 nV\/\u221aHz chopper amplifier using an inverter-based 0.2-V supply input stage","volume":"52","author":"Yaul","year":"2017","journal-title":"IEEE J. Solid State Circuits"},{"key":"ref_11","first-page":"189","article-title":"A simple area-efficient ripple rejection technique for chopped biosignal amplifiers","volume":"62","author":"Chandrakumar","year":"2015","journal-title":"IEEE Trans. Circuits Syst. II Express Briefs"},{"key":"ref_12","first-page":"2811","article-title":"An 80-mVpp linear-input range, 1.6-G\u03a9, low-power chopper amplifier for closed-loop neural recording that is tolerant to 650-mVpp common-mode interference","volume":"52","author":"Chandrakumar","year":"2017","journal-title":"IEEE J. Solid State Circuits"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Wu, R., Huijsing, J.H., and Makinwa, K.A.A. (2013). Precision Instrumentation Amplifiers and Read-Out Integrated Circuits, Springer.","DOI":"10.1007\/978-1-4614-3731-4"},{"key":"ref_14","unstructured":"Tsividis, Y. (1999). Operation and Modeling of the MOS Transitor, McGraw-Hill."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"976","DOI":"10.1109\/JSSC.2003.811973","article-title":"14-bit high-temperature \u03a3\u0394 modulation in standard CMOS","volume":"38","author":"Davis","year":"2003","journal-title":"IEEE J. Solid State Circuits"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"780","DOI":"10.1109\/33.49047","article-title":"Scaling, subthreshold and leakage current matching characteristics in high temperature (25\u2013250 \u00b0C) VLSI CMOS devices","volume":"12","author":"Shoucair","year":"1989","journal-title":"IEEE Trans. Compon. Hybrids Manufact. Technol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"e215","DOI":"10.1161\/01.CIR.101.23.e215","article-title":"PhysioBank, PhysioToolkit, and PhysioNet: Components of a new research resource for complex physiologic signals","volume":"101","author":"Goldberger","year":"2000","journal-title":"Circulation"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"256","DOI":"10.1109\/JSSC.2007.914720","article-title":"Minimum energy tracking loop with embedded DC\u2013DC converter enabling ultra-low-voltage operation down to 250 mV in 65 nm CMOS","volume":"43","author":"Ramadass","year":"2008","journal-title":"IEEE J. Solid State Circuits"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"3119","DOI":"10.1109\/JSSC.2017.2747217","article-title":"A wide dynamic range buck converter with sub-nW quiescent power","volume":"52","author":"Paidimarri","year":"2017","journal-title":"IEEE J. Solid State Circuits"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/7\/2059\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:15:58Z","timestamp":1760174158000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/7\/2059"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,4,6]]},"references-count":19,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2020,4]]}},"alternative-id":["s20072059"],"URL":"https:\/\/doi.org\/10.3390\/s20072059","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,4,6]]}}}