The Research Of SPAD Based ToF 3D Image Sensor's Key Techniques

Time-of-flight 3D image sensor is capable of extracting the depth information of the target,by means of measuring the time interval between the emitted and received signal.Thanks to its straight forward operation principle,it is widely applied in the field of military,medicine,automotive electronics and consumer electronics.When the photon event is sparse,there exists restriction on detection resolution due to the background light.However,the ToF depth imaging systems based on the Time Correlated Single Photon Counting(TCSPC)technique can improved the resolution to picosecond level by multiple sampling the photons.Besides,Single Photon Avalanche Diode has the ability to detect single photon and compatible with CMOS process,it can be adapt to TCSPC structure.So this work focuses on the key techniques of SPAD based ToF 3D image sensor.Based on the TCSPC technique,the high resolution time information quantization method for short range measurement is presented.Analysis of the SPAD working principle and modeling of its dark count rate,afterpulse rate,photon detection probability and dead time is done.The relationship between dark count rate and light responsiveness with different excess voltage is presented as well.The effect of premature edge breakdown has been improved by means of shallow trench isolation.The time quantization circuits are designed.The Charge Pump PLL is designed for stabilize the process,voltage and temperature variation.The layout of the designed circuits has achieved and tapeout in 180 nm CMOS process.Measurement results of the quantization circuits have presented.A SPAD with 10-?m-diameter is achieved in this thesis,it has more responsivity to the 480 nm light.The dark count rate is less than 4 kHz when 1.5V excess voltage is applied.Time resolution of TDCs is 10 ns.The bandwidth of the PLL is 0.6MHz,with the phase margin of 60 degree and 4.5?s set up time.The TDC quantization results under 40 MHz 50% duty cycle square wave is 12.525 ns,the quantization error calculated is 0.202%.