Journal
IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I-REGULAR PAPERS
Volume 64, Issue 10, Pages 2666-2678Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TCSI.2017.2698600
Keywords
Instrumentation amplifier; analog front-end; negative impedance converter; input capacitance cancellation; on-chip calibration; biopotential measurement; negative capacitance generation feedback (NCGFB); test signal generation
Categories
Funding
- National Science Foundation [1349692, 1451213]
- Div Of Electrical, Commun & Cyber Sys
- Directorate For Engineering [1349692] Funding Source: National Science Foundation
- Div Of Electrical, Commun & Cyber Sys
- Directorate For Engineering [1451213] Funding Source: National Science Foundation
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This paper demonstrates an input impedance boosting method that was developed for long-term monitoring of electroencephalography signals. An instrumentation amplifier was designed with a negative capacitance generation feedback (NCGFB) technique to cancel the adverse effects of input capacitances from electrode cables and printed circuit boards. The NCGFB boosts the measured impedance from below 40 M Omega to above 500 M Omega at 50 Hz when the equivalent capacitance at the inputs is up to 150 pF. The prototype chip includes an automatic calibration system to adaptively enhance the input impedance through on-chip test signal generation, measurement, and the automatic digital control of the NCGFB. Consisting of an instrumentation amplifier, a low-pass notch filter, and a variable gain amplifier in 130-nm CMOS technology, the signal path has a combined gain range of 66-93 dB with a total power consumption of 42 mu W. The front-end bandwidth covers 0.5-48 Hz, and its integrated input-referred noise over the bandwidth is 3.75 mu V-rms. The measured third-order harmonic distortion component is at least 57 dB below the fundamental signal level. A common-mode rejection ratio of 77.6 dB and a power supply rejection ratio of 74 dB were measured at 10 Hz. When activated, the auxiliary test signal generation and calibration circuits consume a power of 542 mu W.
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