An asynchronous event-driven data transmitter for wireless ECG sensor nodes

This work presents an asynchronous event-driven transmitter for wireless ECG sensors node. Unlike current solutions for ECG monitoring with autonomous wireless sensors, we propose an asynchronous method to transmit data from an ECG front-end, which is designed with a 2-bit level-crossing analog-to-digital converter. The output bits (UD and Change) of the ADC are first combined using a pulse encoder circuit and then transmitted via a backscattering link in the 402-MHz MICS frequency band. The pulse encoder comprises an inverter delay chain controlled by signal UD, thereby setting the duration of the data pulse. The encoder is enabled only when the ADC has digitized the ECG signal, thus reducing the system´s overall power consumption. The complete IC is designed in a standard 0.18m CMOS process. Simulation results show that the ECG readout plus pulse encoder consumes 9.1μW for 45k data conversions per second.