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A Novel Wideband CMOS Current Driver for Bioimpedance Applications

Neshatvar, N; (2017) A Novel Wideband CMOS Current Driver for Bioimpedance Applications. Doctoral thesis , UCL (University College London).

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Abstract

The variation of tissue’s electrical properties, both dielectric and conductive characteristics, through a frequency spectrum is characterised as bioimpedance spectroscopy. In electrical impedance spectroscopy (EIS) of biological tissues, the overall impedance measurement is performed by applying AC signals, either a current signal or a voltage signal, to the surface of the tissue or cell via one pair of electrodes and recording the resulting signals via a separate or the same pair, which are then converted to impedance via a demodulation process. Considering current stimulus, a wide band current driver up to 3 MHz is desired so that it can penetrate to the nucleolus of the cell and provide accurate information about the morphology and physiology of the cell. This thesis intended to design a novel wide band current driver with phase compensation scheme for tetra-polar EIS applications. It presented the measurement result and experimental validation of the proposed current driver which provide superior performance to the existing state of the art current drivers in terms of bandwidth, output impedance and phase error. The integrated fully differential non-linear feedback current driver is fabricated in 0.35 μm CMOS technology and occupies a silicon area of 1.2 mm2 . With the introduction of automatic phase compensation circuit, the current driver is able to operate at frequencies close to the pole frequency of the output transconductor with phase errors as low as 3o at 3 MHz Frequency. Another important aspect of the phase compensation is that the output impedance of the current driver remains (largely) constant throughout the entire range of operational frequencies (100 kHz – 3 MHz). The current driver can deliver a maximum output current of 1.8 mAp-p from a supply of ± 2.5 V. For an output current of 1 mAp-p the accuracy is 0.24%, 0.43% at 1 and 2 MHz respectively. With active compensation, the phase error at the output of the current driver reduces to 1o at 1 MHz and 3o at 3MHz. The current driver can be configured to operate with multi-frequency (multi-sine) by connecting in parallel extra current drivers (with their corresponding phase compensation).

Type: Thesis (Doctoral)
Title: A Novel Wideband CMOS Current Driver for Bioimpedance Applications
Event: UCL (University College London)
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
URI: http://discovery.ucl.ac.uk/id/eprint/1546168
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