Abstract
This thesis presents a reflective pulse oximetry sensor with DC cancellation and AC amplification scheme. The photodiode integrated sensing chip realizes highly portable and low form factor IoT application. The DC and AC component for both IR and RED LED reflected PPG signal are extracted for oximetry calculation. To extract the small AC component of PPG signal, which is about 0.5%~2% of DC component, with a specific resolution, the current DAC is implemented to not only convert the analog current value into digital code for DC code readout but also directly cancel out the DC component more than 1 second. The residue of PPG signal which is composed of AC component and quantization error is converted from current to voltage domain by capacitive transimpedence amplifier (CTIA), and amplified by programmable gain amplifier (PGA) to meet the ADC input range. The buffered direct injection (BDI) is adopted to decrease the DC gain requirement of CTIA OP due to large photodiode parasitic capacitance. A prototype of 128×64 photodiode integrated reflective pulse oximeter employed these schemes has been designed and fabricated in VIS 0.18um 1P4M standard CMOS technology with a chip area of 3450×2450μm2, operating under 1.8V for both analog and digital circuits. The measurement result shows the proposed reflective pulse oximeter front end achieves 7.271nA/Lux photosensitivity, 1 LSB,rms DC cancellation noise with LSB option 0.4nA, 35.9dB SNR of AC signal with filter which leads to ±0.33% SpO2 variation in ±1σ at SpO2=96%, and finally it achieves 99.8μW power dissipation.