An Analog Front-End for a Photoplethysmography Patch to Monitor Respiratory Rate

This paper proposes the design of an analog frontend to be used in a photoplethysmography application to detect respiration rate and transmit the information using an RF antenna. This signal can then be processed off-chip to extract respiratory rate (RR). The chip is powered using wireless power transfer through the same antenna. The design includes an RF-to-DC converter, an LED driver, a transimpedence amplifier, a low-pass filter, a programmable gain amplifier, and a voltage controlled oscillator. The chip is designed in TSMC 0.18 µ
$m$
CMOS process. The overall power consumption is 2.46 mW from a 3.3/1.8 V source. The input RF power signal, transmitted at a frequency of 13.56 MHz, is converted to a DC voltage using a passive rectifier with a power conversion efficiency of 73.6 %. The TIA has a gain of 113 dB and a bandwidth of 663 kHz. The achieved cutoff frequency of the filter is 5 Hz.