Digital Circuit Simulations

1. Digital Circuit Simulations Deborah Barnett, Tidehaven High School Tidehaven ISD Dr. Peng Li, Assistant Professor (faculty mentor) Department of Electrical and Computer Engineering Texas A & M University Ping-Hsiu Lee, Reagan High School Houston ISD (research partner)

2. THE LAB RESEARCH: THREE MAIN THEMES • FIRST THEME: design automation of electronic circuits and systems, also commonly referred to as VLSI CAD VLSI means Very Large Scale Integration CAD means Computer Aided Design

3. …… • SECOND THEME: built-in self-test of analog/mixed-signal ICs and tunable circuit design, IC means Integrated Circuit • THIRD THEME: parallel methods for large-scale computing problems encountered in integrated circuit design and other computing applications .

4. Current research topics in the Department of Electrical and Computer Engineering Lab: • Parallel VLSI CAD algorithms and their implementation on multicore and distributed platforms

5. ……….and • Tunable design/built-in-self-test/CAD for analog/mixed-signal ICs

6. ……and • CAD for multicore chip designs and embedded memories

7. ……and • Analysis and design of  IC power/ground distribution & clock networks

8. ….and • Massively parallel GPU (Global Processing Unit) computing for VLSI design and general computing applications

9. …..and finally, the one we’re involved in….. • Statistical circuit design, circuit simulation, interconnect and timing

10. BACKGROUND on researchSPICE • Simulation • Program for • Integrated • Circuits • Emphasis

11. SPICE is a powerful general purpose analog circuit simulator that is used to verify circuit designs and to predict the circuit behavior. This is of particular importance for integrated circuits.

12. SPICE was originally developed at the Electronics Research Laboratory of the University of California, Berkeley (1975).

13. PSPICE • PSpice is a SPICE analog circuit and digital logic simulation software that runs on personal computers. It was developed by MicroSim and is used in electronic design automation.

14. MORE BACKGROUND TO KNOW FOR RESEARCH • analog circuit, electronic circuit that operates with currents and voltages that vary continuously with time and have no abrupt transitions between levels.

15. And More …. • Digital circuits are electronic circuits that take on only a finite number of states. • Binary (two-state) digital circuits are the most common.

16. ANALOG vs DIGITAL • Generally speaking, the voltage of analog circuits vary in a continuous manner while when working with digital circuits, we are interested in when the circuit is on or off. In other words, we consider them as a binary circuit.

17. THE BASIC DIGITAL CIRCUIT The basic digital circuit for our research design consists of a pull-down network and a pull-up network. The input and output of the circuit is binary, 0 or 1. (0 for off and 1 for on)

18. THE CIRCUIT For the pull-down network (or nMOS) to be active, the output must be 0. For the pull-up network (or pMOS) to be active, the output must be 1. nMOS means negative Metal Oxide Semiconductor pMOS means positive Metal Oxide Semiconductor

19. Designing a Circuit We need to consider the duality rule for circuit design. The duality rule part 1 : If there is a nMOS on the pull-down, then there will be a pMOS on the pull-up and vice versa.

20. EXAMPLEof a circuit in action when the input is 0 (drain) The duality in this system is shown with the pull-down to ground as nMOS and the pull-up to VDD as pMOS (source)

21. EXAMPLE of a circuit in action when the input is 1

22. More on Duality • Duality Rule part 2: transistors that appear in series in the pull-down network must appear in parallel in the pull-up network and vice versa.

23. Duality Design Parallel transistors pMOS Series transistors nMOS

24. RELEVANCE/REAL WORLD APPLICATION • Computers, calculators, cell phones….. all depend on microchip design to work. We continue to want our technology to work faster and more efficiently. Design is the first step in making it happen.

25. OVERVIEW OF OUR RESEARCHPROJECT OBJECTIVE • Graphically (by hand) design and analyze circuit functionality and performance.

26. MODELING • Model basic CMOS transistor behavior using simple switch models and more sophisticated continuous models. CMOS means Complementary Metal Oxide Semiconductor

27. DATA INTERPRETATION • Verify graphical analysis (our circuit design) and model behavior using the simulation program PSPICE.

28. SUMMARY The design of the microchip is essential to its use in various technologies. To understand the basic design of the integrated circuits, our research will model simple CMOS transistor behavior using simple switch models and other continuous models. We use PSPICE simulation to verify our hand (graphical) analysis of circuit functionality and performance.

29. CLASSROOM PROJECT This will be an integrated curriculum project with English 1, IPC and Algebra 1.

30. CLASSROOM PROJECT The student will • investigate the development of the microchip and its uses in modern technology • construct an electrical transistor and investigate the physical design of the microchip • design simple CMOS transistors • use PSPICE to analyze their designs

31. REFERENCES Lectures, Dr. Peng Li Weste, N. H. E. and Harris, D. (2005) CMOS VSLI Design: A circuits and Systems Perspective. Boston, MA: Pearson, Addison Wesley. www.seas.upenn.edu

32. ACKNOWLEDGEMENTS • Dr. Peng Li, faculty mentor • TAMU E3 participating faculty • National Science Foundation (NSF) • Ping-Hsiu Lee, partner