An Aquatic Wireless Biosensor for Electric Organ Discharge With an Integrated Analog Front End

Abstract

This paper presents a novel wireless underwater data acquisition system for sensing electric organ discharge (EOD) signals generated from the weakly electric fish S. macrurus . Variation in frequency and amplitude of the EOD signals are of interest by biologists to study behavioral and environmental effects on electric organ cells. In order to record the EOD signals, a miniature wearable wireless sensing system is designed for the target fish. The system consists of a custom-designed integrated analog front-end (AFE), an ATmega328p microcontroller unit and a wireless transmitter (TX), as well as a battery with a power management module. In order to save TX power, the wireless sensor only transmits the calculated frequency and amplitude information of the EOD signal based on a proposed gain-feedback control method. A receiver attached to a host computer receives the wirelessly transmitted EOD data to perform further analysis. A wearable waterproof backpack for the fish is designed to house the wireless sensor and battery. The overall system has been successfully tested in a clinical experiment with the weakly electric fish. The AFE integrated circuit, which includes a novel rail-to-rail dynamic comparator, is fabricated in a 0.18- $\mu \text{m}$ CMOS process. The total area of the core circuit is 1.0 mm2. The LNPA achieved a noise efficiency factor of 1.8. The AFE power consumption is 2.2 $\mu \text{W}$ from a single +1.8 V supply, whereas the overall system power consumption is 15 mW. The proposed gain-feedback control structure for frequency and amplitude measurement saves the transmitter data rate by 3,756 times compared with sending the raw data.