Design Of Low-Power Timing Readout Circuit Based On SPAD-TDC Array

As one of the mainstream technologies in 3-Dimensions(3D)imaging applications,TOF ranging imaging technology,based on single photon avalanche photodiode detector(SPAD)and Time-of-Flight(TOF)measurement,due to its advantages of long-range detection,strong anti-interference ability and high accuracy,has played a leading role in cutting-edge applications such as Advanced Driving Assistance System(ADAS),lidar and face recognition.This paper is based on the applications such as flood laser lidar for the requirements of high-precision and low-power tracking detection of wide dynamic range targets.It mainly focuses on the direct TOF(DTOF)ranging imaging technology for long-range detection.Based on the time-to-digital converter(TDC),the digital timing readout circuit(ROIC),as the core module of the DTOF ranging imaging system,is responsible for the functions of generating and readout the pixel TOF encoded data,its performance directly affects the final imaging quality of the system.At present,one of the main disadvantages of DTOF ranging imaging technology compared to the other mainstream 3D imaging technologies such as binocular stereo vision technology and structured light technology is the small size of the pixel array,resulting in fewer pixels in the X-Y axis direction or the lateral resolution of the image after imaging is low,often requiring the use of scanning equipment to expand the spatial resolution,and excessively high ROIC system power consumption as a major factor limiting the expansion of the pixel size waiting to be resolved.In order to meet the ROIC design requirements of real-time detection with wide dynamic range and low power consumption,based on the typical application scenario where the minimum distance of the measured target is usually much larger than the maximum measurable depth of field of the measured target,and on the basis of the classic ROIC,a step-by-step low-power TOF quantification method of separation of the distance and the depth of field is proposed,and complete a new low-power digital timing ROIC system design based on dual-mode switching.The new low-power ROIC can adaptively switch the TOF quantization mode of the next data-collection-frame of the ROIC according to the distance of the measured target within the current data-collection-frame,that is,it can switch the ROIC to work in the classic single-frame quantization mode or the dual-frame multiplexing quantization mode.No matter which TOF quantization mode,the working time of the array-TDC in the pixel is relatively short,the average TOF quantization power consumption is greatly reduced,and the number of data conversion bits of the array-TDC is reduced,the data transmission pressure is also reduced simultaneously,in addition,the limitation of the pixel area on the ROIC timing range is eliminated,and the application flexibility is improved.Compared with the classic ROIC,the new lowpower ROIC in this paper limits the maximum measurable depth of field of the measured target,while slightly increasing the difficulty of data processing,but in return for simultaneous decrease in the average power consumption of the system,data readout pressure and pixel area requirements,the overall performance can be greatly improved,and the greater the detection distance requirement,the higher the energy efficiency of the low-power ROIC in this paper.Under the TSMC 0.18?m 1P6 M CMOS process conditions,the schematic and layout design of the new low-power ROIC proposed in this paper,as well as the pre and post simulation verification and MPW tapeout work were completed.The final total area of the system physical layout is 5231?m × 5221?m.The simulation results show that under the conditions of 1.8/5V power supply voltage,-40 ? operating temperature(SPAD limit),tt process corner,50?m × 50?m pixel area,20 k Hz data acquisition frame rate,250 MHz four high-frequency split-phase quantization reference clock HCK1? HCK4 and 50 MHz data readout clock LCK driving,the ROIC designed in this paper can obtain a time resolution of 500 ps,a timing range of 5?s,and an average system power consumption of only 35 m W,the maximum measurable distance of 750 m and the maximum measurable depth of field of 1.5m are achieved.When tested at room temperature,the average power consumption of a single frame of the low-power ROIC is about 60 m W,which is in good agreement with the simulation results.