ECE 2020 Digital Design

Prof. Matthieu Bloch

Monday, September 15, 2025 (v1.0) - Switches

Last time

  • Last time
    • Kmaps
  • To be effectively prepared for today you should have:
    • Worked on Homework 2
    • Started reviewing the textbook and your notes in preparation for the exam
    • Possibly looked at the problems in the textbook for extra practice
  • Important notes
    • Homework 2 due today (solution will be posted so don't be late)
    • Breanna's office hours Thursdays 2-3pm in TSRB 530
    • First exam on Wednesday September 17, 2025 - don't be late please
      • I will hold office hours before for last minute questions.
  • Today
    • We will talk about the implementation of boolean algebra
  • Be ready!
    • I expect you to take notes
    • We will take a quizz on canvas for attendance

First exam

  • Coverage
    • Everything up to and including K-maps in SOP form
    • I will upload an asynchronous video to discuss POS form but it is out of scope for the exam
    • Homework 1 and Homework 2
  • My expectations
    • You have come to class and you have taken notes
    • You have worked on your homework
    • You will make an effort to write legibly
  • What to expect
    • 3-4 problems in 70 minutes (~15 minutes per problem)
    • You can bring a two-sided sheet of notes - no other materials
    • The problems will not be identical to the homework, but they will be similar
    • At least one problem testing you ability to apply definitions
    • At least one problem involving a proof (i.e., I'll want you to write things formally)
    • At least one problem involving a specification that you will translate into boolean algebra

Switch and Switching Networks

  • Switch as basic building block

  • Let us look at multiple switches connected together

    1. Series
    2. Parallel
    3. Input selector

Controllable switches

  • Our logic needs to be programmable to be useful
  • How do we implement a controllable switch?
    • MOSFETs: Metal Oxide Semiconductors Field Effect Transistors
    • These constitute imperfect switches

Transmission gate

  • Can we build a perfect switch using both nMOS and pMOS?
  • We can create a composite switch
  • We can cerate logic families

High impedance

CMOS

  • CMOS logic: Complementary MOSFET logic family such that pMOSes propagate 1s and nMOSEs propagate 0s
  • How do we implement boolean expressions in CMOS logic?
  • Example: inverter

Until next time

  • To be effectively prepared for your exam on Wednesday September 17, 2025, you should:
    • Read your notes and review the examples
    • Get some sleep before the exam