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Transcript

An Analog Wavelet Transform CMOS Imager Chip Adeel Abbas, Saurav Panda, Vikram Shirgur Graduate Advisor: Shantanu Chakrabartty 520.490 Analog and Digital VLSI Systems Motivations Hardware Implementation of Image Compression Small size Reconfigurable to compute user-defined functions (e.g. Walsh Transform, Hadamard Transform) Edge detection, pattern matching Wavelet Transform Theory Multi-resolution feature extraction Many basis functions available, Haar Wavelet implemented Haar transform is a combination of summing and difference operations Hardware Implementation Haar Transform can be realized as a Matrix Vector Multiplication problem W (i,j) = ( ΣA(i)×P(i,j) ) × B(j) Multiply with either +1, 0 or -1 Inputs are presented in bit-serial fashion System Architecture 16 x 24 pixel array 2 CDS stages for inner and outer products Product coefficients input through shift registers The APS Cell Charge mode implementation Product Coefficient provided in two phases Output of all cells is dumped to a common line Charge is either dumped or extracted from output line The APS Cell (Layout) Uses photodiode type design Susceptible to mismatches in transistor sizing Fill Factor: 60 % Dimensions: 89λ x 89λ CDS Circuit Cascoded inverter used for high gain Phase of B(i) determines whether we connect output capacitor to CDS or Vref CDS stage 1 adds charge across columns, Stage 2 adds output of CDS circuits in stage 1 Complete Schematic Simulation of APS And Inner Product Operating Frequency of 11KHz Photocurrent of 60pA Sequencing of 1st and 2nd stage clocks is very important Here we are multiplying by -1 Simulation Results for Outer Product (4×4) Here again we are multiplying by -1 Output valid during Hold phase of stage 2 Voltage range of 1.76V to 4.23V, with reference at nearly 3 V Complete Layout with Pad-frame Future work Parallel readout (currently can be used as a random-access imager) Extend for a 3 x 3 pad-frame. Would allow a resolution of around 72x72 More test pins. Currently the chip utilizes 29 pins Questions?