Analog VLSI Systems Laboratory







I have designed chips and fabricated them through MOSIS that emulate the early visual processing functions found in vertebrates. The designs are based on the Mead-Mahowald silicon retina. The designs focus on improvements that are intended to remove cell to cell variations that cause errors in the output. The designs we have worked on here also have an optical output, using FLC light modulators. The optical output provides a means for optically connected the chip to another for other processing. View the abstract of the conference paper published discussing the retina designs.

Retina picture See a larger picture of a silicon retina chip I designed and fabricated through MOSIS .

Stereopsis is one method for performing depth perception, which is the ability to determine the relative distance of objects. I have developed a functional stereopsis algorithm based on the Marr theories, and then developed an analog VLSI processor based on that software algorithm. A description of the algorithm is available. This processor is the foundation of a complete visual processing system.

CMOS detectors are the primary optical input devices used in these visual processing circuits. Currently, these are also being studied for use in digital cameras since they can be made in a standard CMOS process. However, noise is a problem when using these devices. I am inveistigating a means for reducing noise using an analog VLSI amplifier.

Analog VLSI Design

The term "analog circuits" usually conjures up images of filters, op amps and A to D converters. Large transistors are the norm, and extremely low noise is the goal. There exists a different branch of analog design: analog VLSI design. This is a small, but growing field that draws principles from both analog and digital design in order to create systems that perform specific functions. From the analog field come the analog components (with some digital components as needed) and analog processing. These analog components are designed to be as compact and dense as possible, squeezing as many processing elements onto a chip as possible; a concept of drawn from digital design. The result is a massively parallel processor that can perform many unique functions. Some examples of these processors are the silicon retina (originally created by Mead and Mahowald), stereopsis processors, robot path planning circuits, and numerous cellular neural network-based circuits.

In my dissertation research, I chose to focus on the development of stereopsis processor that was designed to work in an analog CMOS foundation, yet could easily fit into a more complete model of the visual system. The result was a prototype of this system that was able to determine the relative depth of simple optical inputs. A summary is available.

The biological visual processing system begins with an optical input and ends with neural processing at the highest levels of the brain. Future work involves the development of a complete visual processing system that incorporates many aspects of the human visual system. This will be an analog VLSI system.

Other work I am interested in involves remote testing of VLSI circuits and analog VLSI implementation of conventional computer-based alogrithms.

Neuromorphic Visual Processing Systems Implemented in Analog VLSI (funded by NSF)

Combination of the above two topics along with other visual processing aspects and educational development. This project is funded by the National Science Foundation (NSF).

The project presented in this proposal combines educational and research activities through exploration and development.

The research portion of the work will be formed around the field of analog VLSI systems with an emphasis on neuromorphic processing. A unique approach will be taken to implement an integrated artificial visual system that is formed from distinct components that are designed to work together seamlessly. The entire system will be designed to operate as an entire, functional unit, but will be designed as modular pieces with each piece created individually; the complexity of the visual system requires that it be modeled in manageable pieces. The visual system will consist of the low-level processing functions performed by the retina, mid-level stereopsis processing, and high-level object recognition. The retina function has been implemented successfully, but modifications will be made to previous designs to accommodate the connections to other levels of processing. An analog VLSI stereopsis processor design that has been created will be redesigned to fully take advantage of top-down connections from an object recognition-processing unit. Finally, a unique object recognition system will be designed based on current psycho-physical and biological models of object recognition that is compatible with analog VLSI. The final system will be a silicon-based system that performs multiple visual functions and implemented on an analog VLSI platform. The proposed research will provide new insights into the development of artificial visual systems through the concept of modularization. This type of processing-specific analog circuit is compact and has very low power consumption, making it ideally suited for low cost, high volume, and autonomous exploration devices. Also, this work will generate a set of design standards for analog VLSI, which will aid the mainstreaming of this technology. Students working on the research in this project will gain exposure to diverse fields of science and develop new in-sights into how to model and synthesize complex systems.

The teaching portion of the work will be formed around increasing the use of technology in the classrooms, by addressing the needs of a diverse student body through varied teaching methods, by increasing the understanding of integration and system-level IC design, and by addressing the retention and recruitment problems at the under-graduate and graduate levels, respectively. These objectives are closely linked to one common theme: improving education through commitment. By developing new methods or using the variety of existing methods to transfer knowledge to students, students from all walks of life can find electrical engineering to be exciting and fulfilling. This will be accomplished by continuing to experiment with group learning techniques and alternative forms of evaluation and assessment.

The study of analog VLSI systems requires an understanding of all levels of a system, from transistor physics to amplifier design to IC-level layout issues to board-level interconnections. Students must also have an understanding of these levels and their relationship in order to be successful designers of the more complex systems of the future. These concepts will be reinforced by highlighting integration and system constraints in the core electronics class, by introducing a new IC layout elective class and examining the introduction of layout tools at the freshman level.

The proposed educational plan is closely tied to the research plan by involving undergraduate students in the research projects and by involving research-oriented graduate students in the educational process through guided supervision. The results from the proposed research will be brought to undergraduate students in the form of group projects, case studies for reinforcing core knowledge, and through examples in class. Student portfolios will be explored as means for aiding students in improving their understanding of material through regular assessment By maintaining an up-to-date website intended for elementary and high school students, they will have access to the ongoing research work. Additionally, student-oriented research-based project demonstrations will be developed that will be brought into classrooms to further engage the students as they are formulating their future interests.

I have been involved with the development of a new class room structure based on the model at RPI. Our studio lab incorporates standard laboratory equipment as well as computers and modern visual display equipment. The goal is to improve learning through the integration of lectures, lab experiments, and simulations. View a picture of the studio lab.

I am also involved with the development of novel tools to aid in teaching electronics, and IC design and layout.

last updated: 4/16/03