A 2KSPS 123dB Dynamic-Range SPAD-based Optical Sensor SoC with On-chip Auto-Gain-Control and FFT Processor for 100 μlux Light Illuminance and Flicker Detection

Silicon photodetectors, such as photodiode (PD), are extensively used in optical sensing as their proper performance and low cost to achieve screen brightness adjustment, ambient light flicker detection, and other functions. With the rise of under-screen optical sensing, PD is no longer sufficient for low-light level light detection and real-time low light level flicker detection. While an emerging detector, single photon avalanche diode (SPAD), shows its advantage to ultralow light sensing. However, SPAD tends to saturate at high light levels, which limits its widespread application. To inspire ambient light sensor design and address these issues, this paper proposes a high sample per second (SPS), wide dynamic range (DR) and ultralow illuminance detection SPAD array system on chip (SoC). A $16\times 16$ SPAD array architecture along with counter and charge-pump is designed in 180nm BCD process to sense 100μdux ambient light at 660nm. On-chip FFT processor of 2048 points with 32-bit accuracy is realized to process sampled optical waveform for flicker detection. Besides, an area-efficient integrated charge pump is implemented to regulate high-voltage (19~25V) to SPADs with on-chip digital auto-gain control (AGC), which improves the optical DR from 87db to 123db. This work extends the optical sensing range significantly and demonstrates the effectiveness of the proposed SoC with systematical measurements.