Digital Circuit Simulations

							 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)
                      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
                             ……
• 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 .
         Current research topics
   in the Department of Electrical and
      Computer Engineering Lab:



• Parallel VLSI CAD algorithms
  and their implementation on
  multicore and distributed
  platforms
           ……….and



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

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


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

• Massively parallel GPU (Global
  Processing Unit) computing for VLSI

  design and general
  computing applications
  …..and finally, the one we’re
        involved in…..

• Statistical circuit design,
 circuit simulation, interconnect
 and timing
    BACKGROUND on research
                  SPICE
•   Simulation
•   Program for
•   Integrated
•   Circuits
•   Emphasis
• 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.
• SPICE was originally
  developed at the Electronics
  Research Laboratory of the
  University of California,
  Berkeley (1975).
                 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.
  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.
              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.
       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.
 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)
              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
         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.
    EXAMPLE of a circuit in action when the
                 input is 0

                         A      Y
                                                         VDD     (drain)

                         in     out
                         0      1                               ON
                         1                     A=0               Y=1

        A                      Y                                OFF

                                                         GND
The duality in this system is shown with the         (source)
pull-down to ground as nMOS and the pull-
up to VDD as pMOS
EXAMPLE of a circuit in action when the
             input is 1

 A   Y                  VDD
 0   1
 1   0                    OFF
                 A=1          Y=0

                           ON
A           Y
                        GND
           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.
Duality Design
                Parallel transistors
                    pMOS

          Y
A
B
              Series transistors
                    nMOS
       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.
  OVERVIEW OF OUR RESEARCH
          PROJECT


             OBJECTIVE
• Graphically (by hand) design and analyze
  circuit functionality and performance.
                   MODELING
• Model basic CMOS transistor behavior
  using simple switch models and more
  sophisticated continuous models.

CMOS means Complementary Metal Oxide Semiconductor
    DATA INTERPRETATION
• Verify graphical analysis (our circuit
  design) and model behavior using the
  simulation program PSPICE.
                 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.
  CLASSROOM PROJECT

This will be an integrated
curriculum project with
English 1, IPC and Algebra 1.
     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
            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
      ACKNOWLEDGEMENTS
•   Dr. Peng Li, faculty mentor
•   TAMU E3 participating faculty
•   National Science Foundation (NSF)
•   Ping-Hsiu Lee, partner