A high-performance analog front-end for an intraoral tongue-operated assistive technology

Tongue Drive System (TDS) is a tongue-operated, wireless assistive technology that infers its users´ intentions by detecting their voluntary tongue motions, and translating them into user-defined commands. In this paper, we present the design of a low-power analog front-end (AFE) with configurable characteristics that tracks the tongue motion by reading four intra-oral 3-D magnetic sensors to indicate the position of a small magnet attached to the tongue. Duty cycling is employed as a key feature in this system to reduce power consumption in the sensors and in the low-noise interfacing circuits, allowing for energy savings as much as 92%, which greatly extends the battery life. The AFE has been implemented in a 0.5-μm CMOS process and consumes 7.1 μA per sensor readout from a 1.8/4.2 V supply at a minimum duty cycle of 2%. Post-layout simulations show that the readout channels typically feature a noise density of 57 nV/VHz and a CMRR above 120 dB within the frequency band of interest (DC-2.5 kHz). Moreover, it presents a typical THD of 0.025%, a maximum input-referred offset of 5 μV, and a gain that is independent of temperature and process variations.