A 52 µW Heart-Rate Measurement Interface Fabricated on a Flexible Foil with A-IGZO TFTs

This paper presents a 52 μW heart-rate measurement interface for wearable applications, fabricated on a flexible foil with a-IGZO TFTs. The interface consists of a cascaded diode-connected load preamplifier with a gain of 22 dB in 3 kHz bandwidth. The output is provided as a binary PWM waveform, which can be sent to a reader device using wireless communication. Voltage to pulse-width conversion is achieved with a simple and power minimalistic approach, which exploits a reset integrator. Experimental characterization demonstrates an overall low-frequency gain of the system equal to 25 msec/V and an input referred noise of 186.3 μV rms. In-vivo measurements have been performed, resulting in a 60 bpm heart-rate for a person at rest.