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?