Research On Key Technology Of SPAD Based Flash LiDAR

In recent years,LiDAR has been widely used in assisted driving,smart home,aerial surveying and virtual reality.The LiDAR sensor adopted on the i Phone 12 has detonated the demand for To F sensors in the consumer electronics market.LiDAR is a pair of eyes of smart devices.Compared with traditional image sensors,it can directly provide reliable threedimensional distance information,which can be used for sensing the environment and achieve precise positioning and navigation.With the continuous improvement of the technical,the volume of the LiDAR system is becoming smaller and smaller.One of the most critical technologies is the LiDAR chip technology,which can greatly reduce material costs,improve system performance,and enhance system reliability.Fully integrated solidstate LiDAR is the development trend in the future.In this thesis,we mainly study the chip technology of the receiving end of the LiDAR system.First of all,to set the parameters of the system properly and get a more intuitive understanding of the photoelectric combined system,we use MATLAB to model and simulate the SPAD-based LiDAR system,and analyze the pile-up effect caused by the background light noise.The simulation verifies the effectiveness of spatial-temporal correlation detection method and gating method for noise filtering.A Si PM-based multi-line LiDAR chip and a SPAD-based 256×256 flash LiDAR chip are proposed in this article,and we discuss the key device technology and circuit technology in detail.A 16-line LiDAR chip based on 0.18 ?m HV CMOS technology is proposed at first,which uses a 16-channel Si PM as the photoelectric detection device,and is fully integrated with the corresponding 16-channel analog front-end and TDC circuit.The single-channel Si PM is composed of 16×16 microcells.Each microcell is composed of a SPAD,active quenching circuit and current steering unit.The current steering unit converts the voltage pulse into current pulse,and the output of each microcell is summed up at the output terminal of Si PM,so it not only has the same sensitivity as SPAD,but the output can provide intensity information.The 16-channel analog front-end circuit is composed of a VGA and a comparator,which amplify the output signal and achieve threshold detection,and then the timing information is quantized by the gated ring oscillator based TDC with a resolution of200 ps.Measurement result shows that the chip can achieve a detection accuracy of 3 cm within a range of 20 m.A 256×256 flash LiDAR chip based on 55 nm CMOS technology is also proposed in this work,which uses SPAD as an optoelectronic device to suppress the pile-up effect through the gating method,and the depth resolution and measurement range can be adjusted flexibly.The gating method does not require a macro pixel unit and can achieve higher spatial resolution.A two-step quantization method is used to obtain distance information.The coarse quantization is determined by the number of integer cycles between the gated window and the pulsed laser and the TVC within the pixel converts the residue time information into a voltage value for fine quantization by the column ADC.The simulation results show that the two-step quantization chip can achieve a time resolution of less than 100 ps in the range of 10 m,the field of view is 20°×20°,and the overall layout area is 6.6 mm×6 mm.