Smart Sensor Architecture

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					  Smart Sensor Architecture
for Real-Time High-Resolution
        Range Finding


 Y. Oike, M. Ikeda and K. Asada
       Dept. of Electronic Engineering
  VLSI Design and Education Center (VDEC)
            University of Tokyo
                                       ESSCIRC 2002
                   Contents
Background and Motivation
Sensor Architecture
  Pixel circuit
  Time-Domain Approximate ADC
  Position Encoder
Chip Implementation
Performance Evaluation
  Frame rate
  Sub-pixel accuracy
Application to 3-D measurement
Conclusions
        Background ~ Range Finding System ~
         Many Applications of 3-D Graphics
                   Robot vision, Shape measurement etc…

                   Movies, TV, Video games etc…
            Advanced range finding system is
Input       required for the future applications          display
 expression                             compression
              comprehension transmission
 Robot Vision      Shape Measurement
                   Shape Measurement                  Modeling
                                                      Modeling
                                  Duplication
   Backgrounds ~Triangulation-Based Active Method~
Triangulation-Based Active Range Finding
 advantage
        High accurate 3-D measurement
        Range map can be acquired by a simple calculation
 disadvantage
        Scanning light projection
        A lot of position detections to get a range map
       Motivations ~For Real-Time Range Finding~

Problems of the REAL-TIME active range finding
 Not enough frame rate
  Ex.) Over 30k fps for 1M pixel resolution
 Large pixel circuit
  Ex.) Some high-speed position sensor has over 20 tr./pixel.
 Low sub-pixel accuracy (sheet light projection)

Our Sensor Architecture
 High frame rate enough for real-time range finding
 Compact pixel circuit can be used
 High sub-pixel accuracy by an intensity profile
Sensor Architecture

       High-speed position detector
        • Time-domain approximate ADC
        • Priority Encoder
        • Intensity profile readout Circuit
       Pixel array
        • Standard and compact pixel
       Row select and reset scanners

       Pixel value readout circuit
        • Pixel value readout for 2-D image
        • Column-parallel source follower
                    Pixel Circuit




                                                    0.6µm process
Standard and Compact pixel circuit
     2-D capture mode (a)
        the same as a standard CMOS APS
     3-D capture mode (b)
        Discharging time means VPD at the output node
        Peak detection and address encoding in row
                            Time-Domain Approximate ADC

                                                Select Phase
                                          Self-TriggerPhase
                                                ADC
                                           Precharge Phase
    propagation



    propagation


   output output
    charge            discharge
                  discharge
select            precharge




                                          This slide uses animation
                 Time-Domain Approximate ADC
value encoding



                 High-speed peak detection
                     Compact pixel circuit
                     High-speed readout method
                 High sub-pixel accuracy
                     Approximate ADC
                     Intensity profile for gravity
                     center calculation
                  Position Encoder

                            Priority Encoder
                              Encode the edge address
                              of the peak quickly
                              The intensity profile is
                              read out by the priority
                              decision signal
                              Decision delay : log N



   Left edge   Right edge
High speed encoding in large input number ( log N )
Chip Implementation
        Measurement System




Sheet light scanning (300mW, 635nm)
Control the fabricated sensor and mirror by PC
                 Frame Rate

                               Simulated wave forms
                                   Reset voltage : 2.4V
                                   Read and ADC : 30 ns/row
                                   Address encode : 7.2 ns
                                   Profile readout : 4.3 ns




The ultimate frame rate is 260k fps (2k range map/sec)
             (ex. 31.8 range map/sec in 1024x1024 resolution)
             Measured Intensity Profile
Intensity profile of the sheet light on the sphere-shaped object




       Acquire the intensity profile successfully
               Sub-Pixel Accuracy




Our Method                   The conventional method
Max. error : 2.64 mm         Max. error : 7.61 mm
Standard deviation : 1.18 mm Standard deviation : 2.58 mm
High sub-pixel accuracy using an intensity profile
             Results of Range Finding
Captured image in 2-D mode




Captured image in 3-D mode




                         Reproduced range data and wire frame
                        Results of 3-D Capture
      Target Object




Captured by a digital still camera




Complex-shaped target                3-D image by the present sensor
                        Conclusions

We proposed a smart sensor architecture for real-time
and high-resolution range finding.
                          finding
128 x 128 prototype sensor.
The architecture uses a compact pixel circuit.
                                      circuit
The ultimate frame rate is 2k range map/sec
  It corresponds to over 30 range map/sec in 1024 x 1024 pixel resolution

Higher sub-pixel accuracy is achieved by TDA-ADC.
Both 2-D image and range data have been acquired by
the prototype sensor successfully.