Wideband Fully Differential Current Driver with Optimized Output Impedance for Bioimpedance Measurements

This paper presents a wideband fully differential current driver architecture suitable for bioimpedance measurements. It uses an improved regulated cascode to enhance output impedance, enabling accurate measurements of transfer impedances at low and high frequencies. The current driver architecture maximizes the output voltage swing. An independent reference voltage is used in order to compensate the process variations of the output common mode voltage. The circuit was designed in 0.18μm CMOS AMS process, operating from 1.8V supply voltage. The silicon area is 0.26 mm2. The current driver has a 67 MHz bandwidth and can provide a maximum output current of 600 μA peak to peak with a Total Harmonic Distortion (THD) below 0.3% at low frequencies increasing to 0.6% at 8 MHz. Due to the use of regulated cascodes in the output stage, the circuit achieves a 79MΩ output impedance at low frequencies decreasing to 324KΩ at 1MHz, with an output voltage swing of 0.95 V.

Keyword(s)

Operational Transconductance Amplifier, bioimpedance, current driver, regulated cascode

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Lamlih Achraf, Freitas Philippe, David-Grignot Stephane, Salles Jereme, Kerzerho Vincent, Soulier Fabien, Bernard Serge, Rouyer Tristan, Bonhommeau Sylvain (2018). Wideband Fully Differential Current Driver with Optimized Output Impedance for Bioimpedance Measurements. 2018 IEEE International Symposium on Circuits and Systems (ISCAS), Florence, 2018. Electronic ISSN: 2379-447X. pp. 1-5.. https://doi.org/10.1109/ISCAS.2018.8351464, https://archimer.ifremer.fr/doc/00439/55087/

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