Design Of Indirect Time-Of-Flight Ranging System Based On SPAD

With the increasing demand for three-dimensional vision in the fields of autonomous driving,face recognition,3D modeling,and virtual reality in recent years,three-dimensional vision has gradually become a relatively popular research direction.After Apple and OPPO successively launched 3D Structured Light Face ID mobile phones,the market for 3D image sensors has become more popular.Among the many3 D imaging technologies,such as Stereo Vision,Structured Light,and Time-Of-Flight(TOF),the Time-Of-Flight method is favored by researchers for its advantages of resist strong ambient light interference,detection accuracy,detection distance,system integration and cost.Time-Of-Flight ranging is divided into Direct Time-Of-Flight ranging and Indirect Time-Of-Flight ranging,and the Indirect Time-Of-Flight ranging method uses the phase difference between the emitted light and the reflected light to calculate distance information.This method is widely used in the fields of face recognition,3D modeling,virtual reality and other fields due to its high accuracy and resistance to ambient light interference.In this paper,the Indirect Time-Of-Flight ranging system based on SPAD is implemented on SMIC 180 nm CIS technology.The ranging system uses SPAD as the pixel structure of I-TOF,which has better photon sensitivity and quantum efficiency than traditional I-TOF ranging systems with pixel structures such as PPD and CCD,and can effectively reduce laser power to lessen overall device power consumption.In the phase acquisition and readout circuit based on the SPAD phase ranging system,the design structure of the digital circuit is adopted in this paper to improve the phase data acquisition and readout speed,so as to improve the frame rate of the ranging sensor.In terms of the circuit and SPAD device design of the ranging system,in order to address the problems of premature breakdown and DCR of SPAD,this paper designs a SPAD pixel with STI + PW protection ring.In addition,multiple SPADs areemployed to form macro-pixels for coincidence detection to filter non-photon triggering events caused by factors such as DCR and afterpulses.This paper also specially designs a quenching circuit with 5ns dead time,1ns reset time and reset control protection.Finally,based on the design of the indirect Time-Of-Flight ranging system,this paper uses SMIC 180 nm CIS process to realize the indirect Time-Of-Flight ranging sensor based on 4X4 pixel array.The sensor includes a pixel array,a digital timing control,and a readout circuit.The total area of sensor is about 0.872 mm.The sensor's modulated light frequency is 20MHz-40 MHz,and the overall power consumption is about 568.3m W.