OPTICAL FLOW

1
MOTION TRACKING CAMERA
PROJECT DEMO April 19, 2007 1000am, 1030am,
1100am 1130 am, 300pm
Reset Switch Resets the photodiode to a reset
voltage for the next frame
Output Amplifiers Convert output voltage to
electrical current
X and Y Control Registers Allow control of
individual pixels
GROUP 8 AUTHORS Nathan Lazarus
EE07 Sharanya Srinivasan EE07 Lucy Zhang
EE07 ADVISORS Professor Jan Van der
Spiegel Dr. Viktor Gruev Mr. Zheng
Yang ABSTRACT In the field of robotics, research
has become focused on creating mobile,
unsupervised robots to perform various tasks.
From the car-sized vehicles of the DARPA Grand
Challenge to the Predator drones in Afghanistan
and Iraq, sophisticated algorithms have achieved
great advances. However, these algorithms become
a limitation as the focus changes to the smaller
battery-powered robots used in many applications.
Large, power hungry microprocessors become
impossible. This project is focused on
designing a compact low power image sensor chip
able to perform on-chip calculations of optical
flow. Optical flow, the apparent motion in an
image, can be used to control vehicle motion and
avoid obstacles. Light intensity is converted
to electrical current through an array of
photopixels. A series of arithmetic circuits are
then used to calculate the spatial and temporal
derivatives, as well as take their ratio to
calculate the optical flow. SENSOR
CHARACTERISTICS Size of Chip 3mm x
3mm Resolution 84 by 41 pixels Frame Rate 30
Hz Transistors 55932 Input/Output Pins 68
OPTICAL FLOW The optical flow is a measure of
the change in an image from one frame to the
next. It is displayed using a vector field
where each vector represents the apparent
velocity originating at that point. The above
example shows a simple demonstration of the
concept of optical flow . The left two pictures
show two frames the two images show a circle
expanding over time. The right picture shows the
optical flow from the image, consisting of a
number of vectors expanding outward between the
circles. Optical flow is calculated by taking the
ratio of the spatial derivative and the time
derivative in both the x and y directions and
combining these components to form a velocity
field
Photodiode Converts light intensity to voltage
Sample and Hold Circuit Remembers previous frame
Processing Unit Digitally programmable circuit
that can implement a variety of digital filters,
including the first derivatives shown here.
Division Unit Absolute value and unsigned
division circuits to calculate the final optical
flow.
INTEGRATED CIRCUIT DESIGN FLOW
SYSTEM DESIGN The image sensor is the
centerpiece of the camera, but is by no means the
only component. A complete camera needs
microcontrollers, voltage regulators, and
digital-to-analog converters (DACs) to provide
control signals and voltages for the sensor. It
also needs operational amplifiers and
analog-to-digital converters (ADCs) to convert
the output into a usable signal for the computer.

Output operational amplifiers
MAX118 eight channel ADC
MAX5240 four channel DAC
Image sensor and lens
DESIGN AND LAYOUT Because an integrated chip
can contain thousands or even millions of
components, sophisticated computer aided design
(CAD) tools were used to design, simulate, and
layout the sensor.
FABRICATION The design is then sent to a
semiconductor foundry for manufacture The sensor
used an AMI Semiconductor process capable of
feature sizes as small as 0.5 microns.
TESTING AND CALIBRATION The sensor must then be
calibrated to obtain a usable image there are
over 30 input signals and voltages, each must be
carefully timed or set.
SX28 microcontrollers