Ambient Light Rejection Method for SPAD-Based Optical Wireless Communications

Single-Photon Avalanche Diodes or SPADs are gaining popularity as photodetectors for Optical Wireless Communication (OWC) receivers due to their ability to detect single photons resulting in an increased sensitivity. Despite the superior sensitivity, challenges still arise when operating the receiver at high levels of ambient light, where it becomes difficult to distinguish the incident signal photons from the ambient photons, even when using an optical bandpass filter. In this work, a time-correlated method is proposed combining SPADs with switched capacitors, allowing efficient rejection of ambient photon counts without the use of an additional optical filter. A compact 10×10 SPAD-array was designed in 180-nm CMOS technology and tested at different values of ambient light. Open eye diagrams were obtained at 1.2 Mbps with an ambient light level of 100 klx achieving a signal-to-noise ratio of 17.9 dB and a bit error rate below 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup>.