A SPAD Image Sensor With Main-Sub-TDC-Based Coincidence Detection

Light detection and ranging (Lidar) is usually enabled by Single-Photon Avalanche Detector (SPAD) sensors which may be falsely triggered by ambient light. Coincidence detection can suppress the ambient light at the cost of the lateral resolution. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$64\times 64$ </tex-math></inline-formula> SPAD image sensor with coincidence detection is proposed for Lidar. A main-sub time-to-digital converter (TDC), in which the main TDC is used for timestamping the coincidence window and the sub-TDC is used for timestamping the event within the coincidence window, is proposed to avoid the loss of the lateral resolution at a small power cost. A delay-locked loop (DLL) is adopted to generate an analog voltage for maintaining the length of the coincidence window against process-voltage-temperature (PVT) variations. A TDC code correction circuit is proposed to reduce the probability of TDC inter-segment errors to 0.7%. The SPAD image sensor is based on the 3D integration of a SPAD array with a ROIC. The ROIC chip is fabricated in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18\mu $ </tex-math></inline-formula>m CMOS process. Driven by a 250 MHz multi-phase clock and a 100 MHz data readout clock, the chip achieves a maximum frame rate of 35.7 kframe/s, a timing resolution of 0.5 ns, and a timing range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\mu $ </tex-math></inline-formula>s. The typical average power consumption of the ROIC is 135.5 mW (@21.7 kframes/s). The measured differential nonlinearity (DNL) ranges from -0.74 to +0.82 least significant bit (LSB), and the integral nonlinearity (INL) ranges from -0.95 to +0.95 LSB.