{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,17]],"date-time":"2026-06-17T01:30:46Z","timestamp":1781659846272,"version":"3.54.5"},"reference-count":30,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2020,4,7]],"date-time":"2020-04-07T00:00:00Z","timestamp":1586217600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"the Foundation for Young Talents in Higher Education of Guangdong","award":["2018KQNCX405"],"award-info":[{"award-number":["2018KQNCX405"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This paper proposes a compact, high-linearity, and reconfigurable continuous-time filter with a wide frequency-tuning capability for biopotential conditioning. It uses an active filter topology and a new operational-transconductance-amplifier (OTA)-based current-steering (CS) integrator. Consequently, a large time constant    \u03c4   , good linearity, and linear bandwidth tuning could be achieved in the presented filter with a small silicon area. The proposed filter has a reconfigurable structure that can be operated as a low-pass filter (LPF) or a notch filter (NF) for different purposes. Based on the novel topology, the filter can be readily implemented monolithically and a prototype circuit was fabricated in the 0.18 \u03bcm standard complementary-metal\u2013oxide\u2013semiconductor (CMOS) process. It occupied a small area of 0.068 mm2 and consumed 25 \u03bcW from a 1.8 V supply. Measurement results show that the cutoff frequency of the LPF could be linearly tuned from 0.05 Hz to 300 Hz and the total-harmonic-distortion (THD) was less than \u221276 dB for a 2 Hz, 200 mVpp sine input. The input-referred noises were 5.5 \u03bcVrms and 6.4 \u03bcVrms for the LPF and NF, respectively. A comparison with conventional designs reveals that the proposed design achieved the lowest harmonic distortion and smallest on-chip capacitor. Moreover, its ultra-low cutoff frequency and relatively linear frequency tuning capability make it an attractive solution as an analog front-end for biopotential acquisitions.<\/jats:p>","DOI":"10.3390\/s20072065","type":"journal-article","created":{"date-parts":[[2020,4,8]],"date-time":"2020-04-08T05:59:47Z","timestamp":1586325587000},"page":"2065","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["An Area-Efficient and Highly Linear Reconfigurable Continuous-Time Filter for Biomedical Sensor Applications"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7397-0647","authenticated-orcid":false,"given":"Jinyong","family":"Zhang","sequence":"first","affiliation":[{"name":"College of Big Data and Internet, Shenzhen Technology University, Shenzhen 518118, China"},{"name":"Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong 999077, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shing-Chow","family":"Chan","sequence":"additional","affiliation":[{"name":"Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong 999077, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hui","family":"Li","sequence":"additional","affiliation":[{"name":"Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nannan","family":"Zhang","sequence":"additional","affiliation":[{"name":"School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen 518172, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7033-9806","authenticated-orcid":false,"given":"Lei","family":"Wang","sequence":"additional","affiliation":[{"name":"Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,4,7]]},"reference":[{"key":"ref_1","unstructured":"Baghini, M.S., Lal, R.K., and Sharma, D. (2005, January 1\u20133). A low-power and compact analog CMOS processing chip for portable ECG recorders. Proceedings of the 2005 IEEE Asian Solid-State Circuits Conference, Hsinchu, Taiwan."},{"key":"ref_2","unstructured":"Zhang, J., Wang, L., Yu, L., Yang, Y., Zhang, Y.-T., and Li, B. (2009, January 3\u20136). A low-offset analogue front-end IC for multi-channel physiological signal acquisition. Proceedings of the 2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Minneapolis, MN, USA."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1391","DOI":"10.1109\/82.899631","article-title":"A 60-dB dynamic-range CMOS sixth-order 2.4-Hz low-pass filter for medical applications","volume":"47","author":"Maloberti","year":"2000","journal-title":"IEEE Trans. Circuits Syst. II Express Briefs"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Bronzino, J.D. (2000). The Biomedical Engineering Handbook, CRC Press. [2nd ed.].","DOI":"10.1201\/9781003040682"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"91","DOI":"10.1109\/TBME.1973.324169","article-title":"60-Hz Interference in Electrocardiography","volume":"20","author":"Huhta","year":"1973","journal-title":"IEEE Trans. Biomed. Eng."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2774","DOI":"10.1109\/TCSI.2018.2808361","article-title":"A Subthreshold Buffer-Based Biquadratic Cell and its Application to Biopotential Filter Design","volume":"65","author":"Thanapitak","year":"2018","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Lee, Y.-C., Hsu, W.-Y., Huang, T.-T., and Chen, H. (November, January 31). A compact Gm-C filter architecture with an ultra-low corner frequency and high ground-noise rejection. Proceedings of the 2013 IEEE Biomedical Circuits and Systems Conference (BioCAS), Rotterdam, The Netherlands.","DOI":"10.1109\/BioCAS.2013.6679703"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2729","DOI":"10.1109\/JSSC.2006.884195","article-title":"A Micropower Chopper-Stabilized Operational Amplifier Using a SC Notch Filter with Synchronous Integration inside the Continuous-Time Signal Path","volume":"41","author":"Burt","year":"2006","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"762","DOI":"10.1049\/el:19970553","article-title":"Integrated SC low pass filter with a 1-100 Hz variable bandwidth","volume":"33","author":"Gnudi","year":"1997","journal-title":"Electron. Lett."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1392","DOI":"10.1109\/JSSC.2011.2126370","article-title":"A micro power low-noise neural recording front-End circuit for epileptic seizure detection","volume":"46","author":"Qian","year":"2011","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_11","unstructured":"Xu, X., Zou, X., Yao, L., and Lian, Y. (2008, January 18\u201320). A 1-V 450-nW fully integrated biomedical sensor interface system. Proceedings of the 2008 IEEE Symposium on VLSI Circuits, Honolulu, HI, USA."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"776","DOI":"10.1109\/JSSC.2002.1004583","article-title":"A CMOS transconductance amplifier architecture with wide tuning range for very low frequency applications","volume":"37","author":"Veeravalli","year":"2002","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1522","DOI":"10.1109\/JSSC.2007.899081","article-title":"A Fully Integrated Single-Ended 1.5\u201315-Hz Low-Pass Filter with Linear Tuning Law","volume":"42","author":"Bruschi","year":"2007","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1254","DOI":"10.1109\/4.261999","article-title":"Design of a low-distortion 22-kHz fifth-order Bessel filter","volume":"28","author":"Moon","year":"1993","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"2642","DOI":"10.1109\/TCSI.2005.857767","article-title":"A near-infrared heart rate measurement IC with very low cutoff frequency using current steering technique","volume":"52","author":"Wong","year":"2005","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"231","DOI":"10.1007\/s10470-005-3007-x","article-title":"A CMOS Continuous-Time Low-Pass Notch Filter for EEG Systems","volume":"44","author":"Qian","year":"2005","journal-title":"Analog. Integr. Circuits Signal Process."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1109\/TBCAS.2008.2007423","article-title":"Systematic Design and Modeling of a OTA-C Filter for Portable ECG Detection","volume":"3","author":"Lee","year":"2009","journal-title":"IEEE Trans. Biomed. Circuits Syst."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1049\/ip-cds:20000055","article-title":"CMOS transconductance amplifiers, architectures and active filters: A tutorial","volume":"147","year":"2000","journal-title":"IEE Proc.\u2014Circuits Devices Syst."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"2145","DOI":"10.1109\/TCSI.2008.2012218","article-title":"Highly linear tunable CMOS low-pass filter","volume":"56","author":"Acosta","year":"2009","journal-title":"IEEE Trans. Circuit Syst. I Reg. Pap."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1843","DOI":"10.1109\/4.173114","article-title":"A 10.7-MHz 68-dB SNR CMOS continuous-time filter with on-chip automatic tuning","volume":"27","author":"Steyaert","year":"1992","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"166","DOI":"10.1109\/4.278337","article-title":"Integrated continuous-time filter design\u2014An overview","volume":"29","author":"Tsividis","year":"1994","journal-title":"IEEE J. Solid-State Circuits"},{"key":"ref_22","unstructured":"Razavi, B. (2001). Design of CMOS Analog Integrated Circuits, McGraw-Hill."},{"key":"ref_23","unstructured":"(2019, September 30). Available online: https:\/\/www.cadence.com\/content\/cadence."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Abdelhalim, K., and Genov, R. (2012, January 20\u201323). Compact chopper-stabilized neural amplifier with low-distortion high-pass filter in 0.13 \u00b5m CMOS. Proceedings of the 2012 IEEE International Symposium on Circuits and Systems, Seoul, Korea.","DOI":"10.1109\/ISCAS.2012.6271415"},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Wambacq, P., and Sansen, W. (1998). Distortion Analysis of Analog Integrated Circuits, Springer.","DOI":"10.1007\/978-1-4757-5003-4"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1746","DOI":"10.1109\/TCSI.2018.2885954","article-title":"A Nanopower Biopotential Lowpass Filter Using Subthreshold Current-Reuse Biquads With Bulk Effect Self-Neutralization","volume":"66","author":"Sawigun","year":"2018","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"239","DOI":"10.1049\/iet-cds.2018.5002","article-title":"Widely tunable low-pass gm\u2014C filter for biomedical applications","volume":"13","author":"Krishna","year":"2019","journal-title":"IET Circuits Devices Syst."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1268","DOI":"10.1016\/j.mejo.2013.08.013","article-title":"Measured hyperbolic-sine(sinh) CMOS results: A high-order 10 Hz-1 kHz notch filter for 50\/60Hz noise","volume":"44","author":"Kardoulakia","year":"2013","journal-title":"Microelectron. J."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"703","DOI":"10.1109\/TBCAS.2013.2245506","article-title":"A Highly linear fully integrated power line filter for biopotential acquisition systems","volume":"7","author":"Alzaher","year":"2013","journal-title":"IEEE Trans. Biomed. Circuits Syst."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"2666","DOI":"10.1109\/TCSI.2017.2698600","article-title":"An Analog Front-End Chip With Self-Calibrated Input Impedance for Monitoring of Biosignals via Dry Electrode-Skin Interfaces","volume":"64","author":"Chang","year":"2017","journal-title":"IEEE Trans. Circuits Syst. I Regul. Pap."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/7\/2065\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:16:05Z","timestamp":1760174165000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/7\/2065"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,4,7]]},"references-count":30,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2020,4]]}},"alternative-id":["s20072065"],"URL":"https:\/\/doi.org\/10.3390\/s20072065","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,4,7]]}}}