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Impedance Spectroscopy Based on Linear System Identification
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.ORCID iD: 0000-0003-0565-9907
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.ORCID iD: 0000-0003-3802-7834
2019 (English)In: IEEE Transactions on Biomedical Circuits and Systems, ISSN 1932-4545, E-ISSN 1940-9990, Vol. 13, no 2, p. 396-402Article in journal (Refereed) Published
Abstract [en]

Impedance spectroscopy is a commonly used mea-surement technique for electrical characterization of a sample-under-test over a wide frequency range. Most measurementmethods employ a sine wave excitation generator, which implies apoint-by-point frequency sweep and a complex readout architec-ture. This paper presents a fast, wide-band, measurement methodfor impedance spectroscopy based on linear system identification.The main advantage of the proposed method is the low hardwarecomplexity, which consists of a 3-level pulse waveform, aninverting voltage amplifier and a general purpose ADC. A proof-of-concept prototype, which is implemented with off-the-shelfcomponents, achieves an estimation fit of approximately 96%.The prototype operation is validated electrically using knownRC component values and tested in real application conditions.

Place, publisher, year, edition, pages
IEEE, 2019. Vol. 13, no 2, p. 396-402
Keywords [en]
Impedance spectroscopy, system identification, adaptive filtering, pseudo-random waveform, IIR filter, ARX.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-244757DOI: 10.1109/TBCAS.2019.2900584ISI: 000462410800012PubMedID: 30794518Scopus ID: 2-s2.0-85061964097OAI: oai:DiVA.org:kth-244757DiVA, id: diva2:1291356
Funder
Swedish Research Council
Note

QC 20190301

Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2019-04-23Bibliographically approved
In thesis
1. Circuit Design Techniques for Implantable Closed-Loop Neural Interfaces
Open this publication in new window or tab >>Circuit Design Techniques for Implantable Closed-Loop Neural Interfaces
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Implantable neural interfaces are microelectronic systems, which have the potential to enable a wide range of applications, such as diagnosis and treatment of neurological disorders. These applications depend on neural interfaces to accurately record electrical activity from the surface of the brain, referred to as electrocorticography (ECoG), and provide controlled electrical stimulation as feedback. Since the electrical activity in the brain is caused by ionic currents in neurons, the bridge between living tissue and inorganic electronics is achieved via microelectrode arrays. The conversion of the ionic charge into freely moving electrons creates a built-in electrode potential that is several orders of magnitude larger than the ECoG signal, which increases the dynamic range, resolution, and power consumption requirements of neural interfaces. Also, the small surface area of microelectrodes implies a high-impedance contact, which can attenuate the ECoG signal. Moreover, the applied electrical stimulation can also interfere with the recording and ultimately cause irreversible damages to the electrodes or change their impedance. This thesis is devoted to resolving the challenges of high-resolution recording and monitoring the electrode impedance in implantable neural interfaces.

The first part of this thesis investigates the state-of-the-art neural interfaces for ECoG and identifies their limitations. As a result of the investigation, a high-resolution ADC is proposed and implemented based on a ΔΣ modulator. In order to enhance performance, dynamic biasing and area-efficient switched-capacitor circuits were proposed. The ΔΣ modulator is combined with the analog front-end to provide a complete readout solution for high-resolution ECoG recording. The corresponding chip prototype was fabricated in a 180 nm CMOS process, and the measurement results showed a 14-ENOB over a 300-Hz bandwidth while dissipating 54-μW.

The second part of this thesis expands upon the well-known methods for impedance measurements and proposes an alternative digital method for monitoring the electrode-tissue interface impedance. The proposed method is based on the system identification technique from adaptive digital filtering, and it is compatible with existing circuitry for neural stimulation. The method is simple to implement and performs wide-band measurements. The system identification was first verified through behavioral simulations and then tested with a board-level prototype in order to validate the functionality under real conditions. The measurement results showed successful identification of the electrode-electrolyte and electrode-skin impedance magnitudes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 72
Series
TRITA-EECS-AVL ; 2019:33
Keywords
Neural interface, ECoG, high-resolution, ADC, recording, delta-sigma modulator, system identification, impedance measurements
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-249435 (URN)978-91-7873-151-0 (ISBN)
Public defence
2019-05-17, Ka-Sal B (Sal Peter Weissglas), Kistagången 16,, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Note

QC 20190412

Available from: 2019-04-12 Created: 2019-04-12 Last updated: 2019-04-12Bibliographically approved

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Ivanisevic, NikolaRodriguez, SaulRusu, Ana

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