CMOS PPG Readout System with Integrated Temperature and Skin Pigmentation Correction

There is a growing body of research on the effect of skin pigmentation and environmental temperature on blood oxygen measurement, which is a crucial parameter for assessing patients’ respiratory and cardiovascular health. This paper presents an on-chip readout system that utilizes a 4-bit Flash ADC to control gain. The skin-pigmentation feedback controls a programmable gain amplifier in an initialization phase before normal operation and data processing. This correction system has a dynamic range of 60dB and consumes 340 μW of power. The system also counteracts ambient temperature variation via an ultra-low-power sensor, compensating for gain variations. The temperature-to-frequency converter uses 10.8μW and reduces variations in the temperature range of -40°C to 150°C from %22 to %1.3. The overall system, implemented in 45nm CMOS technology, consumes an area of 0.00456 mm
²
. A 200-point Monte Carlo simulation shows no failure due to corners and variations.