An Asynchronous Projection and Summation Circuit for In-Pixel Processing in Single Photon Avalanche Diode Sensors

An asynchronous projection and summation circuit is proposed for single photon avalanche diode (SPAD) sensors. Thanks to the efficient interconnection by the asynchronous technique, the circuit can be easily implemented inside 2D SPAD arrays. As a result, the precise summation of the 1b data in one row can be parallel processed for all rows within the same cycle. A test-of-concept chip was fabricated in a 1P5M 0.18 μm CMOS process. By measurement results, the summation of a 15-pixel row can be achieved by the proposed circuit within 22 ns. Such a speed is very important for SPAD-based sensors that need fast summation operations.