An EMG Interface Comprising a Flexible a-IGZO Active Electrode Matrix and a 65-nm CMOS IC Enrico Genco, Student Member , IEEE, Carmine Garripoli , Jan-Laurens P. J. van der Steen, Gerwin H. Gelinck , Sahel Abdinia

Abstract

In this work, a 4 × 4 active electrode (AE) matrix integrated on a flexible foil substrate to monitor muscular contraction is presented. The electrodes and their front ends (FEs) (i.e., AEs) are implemented on foil in amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) technol- ogy and interfaced with a custom 65-nm CMOS chip where analog-to-digital conversion and serial transmission of data from multiple channels are performed. On-foil frequency multiplexing and conversion to current domain are used to transmit to the silicon (Si)-IC, all the signals coming from a column of elec- trodes via a single output. This strategy enables interfacing the 26-V-supply flexible electronics with the 1.2-V-supply CMOS IC, while reducing the number of interconnects and Si area devoted to pads. The a-IGZO FE includes an integrated switched- capacitor high-pass input filter offering a 25–40-M impedance in the band of interest. Each AE on foil occupies 4 × 4 mm, enabling electromyography (EMG) measurements with millime- ter (mm)-range resolution. The a-IGZO amplifier in the AE, with its intrinsic bandpass response, achieves a process and temperature-insensitive 20-dB in-band gain and a 23-dB dc rejec- tion. The back-end Si-IC can compensate variable bias currents and offsets from the flexible FE exploiting an offset-compensated trans-impedance amplifier (TIA) with 50-dB-dc rejection and negligible noise contribution. The a-IGZO FE alone achieves 20-µA/V gain, 30-kHz bandwi