An Adaptive ASIC for Closed-Loop Low-Power Pulse-Based Ultrasonic Data Transmission

Low-power and robust wireless communication is needed in implantable medical devices with the millimeter (mm) dimension, in which power is scarce. This paper presents an adaptive ASIC for low-power (and robust) data transmission from a mm-sized implant to an external unit using optimal number of ultrasonic (US) pulses. Any changes in the distance and alignment of a US transducer pair (for US wireless power and data transfer) can drastically vary the amplitude of the received signal. To mitigate this issue (i.e., improving robustness) and minimize the power consumption of the data transmitter, the number of transmitted US pulses is changed based on the received voltage at the external unit in the proposed closed-loop system. The proposed ASIC, designed and fabricated in a 0.35 \mu \mathrm{m} standard CMOS process, includes a power-management unit for rectification, regulation, and over-voltage protection of a 1.1 MHz US power carrier using only one external capacitor. The ASIC also includes a pulse-based data transmitter that can adaptively generate 1-8 pulses based on the received pattern modulated on the power carrier. Simulation results demonstrate the functionality of the ASIC in wireless power and data transfer with optimal number of pulses in the implant.