A Linear 126-dB Dynamic Range Light-to-Frequency Converter with Dark Current Suppression Upto 125 °c for Blood Oxygen Concentration Detection

This paper presents a high linear dynamic range light-to-frequency converter (LFC) with integrated photodiodes (PDs). The high dynamic range with linear response is achieved by two techniques. At first, the NWell/PSubstrate PD is regulated to almost zero voltage drop, in order to minimize the bias-dependent leakage current under a low light irradiance. Secondly, a replica amplifier is implemented to monitor the offset voltage of the regulator against process-voltage-temperature variation. As the result, the systematic and layout-dependent input offset voltage of the regulator can be reduced. The proposed LFC chip is fabricated using 0.35- μm 2-poly-3-metal nonepitaxy CMOS technology with a die size of 1.02 × 0.83 mm². According to the measurement results, the proposed LFC is much less sensitive to temperature variation and it exhibits more than six orders of magnitude linear response under the light irradiance as low as 0.5 nW/cm² with a temperature range from -25 °C to 125 °C.