The time stamped architecture for CMOS visual motion sensors

A new time stamped structure for 2D visual motion detection is proposed. In this structure, each pixel records asynchronously the transient time of the motion edges, then the information are read out frame by frame for post processing. This architecture is less sensitive to the pixel level device mismatches in previous velocity sensors while does not have the readout bottleneck problem in previous event-driven readout structures. Measured results show that the proposed pixel design can capture motion in more than 100 times higher time resolution than the frame rate. This enables much higher speed motion detection and greatly reduces the data transfer and computation load of the following digital processor. Totally four CMOS IC chips are fabricated for this research, from the device level photosensor test chip, proof-of-concept time stamped visual motion sensor chip, to several optimized versions of 2D visual motion sensors. The 1st version CMOS 0.35mum 2D sensor verifies the feasibility. The 2nd version 2D sensor achieves 76dB intro-scene linear speed measurement range, less than 5% rms variation for middle speed and less than 10% rms variation for high and low speed, using a new spatial based edge detector. The tested 3rd version 2D sensor reduced the pixel size by half using a new temporal based edge detector. The tested 4th version 2D sensor further reduced the pixel power consumption more than 1000 times than the 2nd and 3rd version. From these test chips, some major improvements have been achieved compared with most recent related previous works, including, (1) reduced pixel size 18 times; (2) reduced pixel power consumption 5000 times; (3) increased intro-scene linear dynamic range for speed measurement 25 times; (4) improved the speed measurement accuracy 1.5 times for middle range speed measurement, and 3 times for high and low speed measurement. It achieved the smallest pixel size and lowest power dissipation ever so as to be promising to implement mega-pixel 2D motion sensor array in the near future. Furthermore, the time stamped structure has been successfully expanded to digital imager design, which largely extended dynamic range for both strong and weak light.