ECE 171: Introduction to Digital Circuits

Fall 1999

Rev: 9.30.99

Lecture Notes 1

This Time

• List of topics for course.
• List of applications that will be discussed.
• Engineering prefixes
• Flashlight Circuit
• Electrical Units
• Analogies
• Symbols
• Ohm's Law
• Power
• Series Resistors
• Parallel Resistors

Topics

• Introduction to analog circuits
• Fundamental logic gates
• Boolean Algebra
• Data Sheets
  • Traditional Symbols
  • IEEE/ANSI Symbols
  • Voltage, Current, & Power Specifications
  • Timing Specifications
• Truth Tables
• Karnaugh Maps
• Circuit Implementation
• MSI & LSI Devices
  • Switches
  • Multiplexer, Demultiplexers
  • PROMs & PALs
• Devices with memory
  • Flip flops
  • Latches
  • Counters
  • Shift Registers

Applications

• Circuit analysis, design, & simplification
• Code conversion
• Counters w/LED Display
• Parallel to Serial & vice versa (for digital communications)
• Music/Sound Synthesis
• Timers & Stopwatches
• Alarm Clocks
• Frequency Counters

This Time

• Common engineering prefixes
  • p = pico = 10^-12
  • n = nano = 10^-9
  • mu = micro = 10^-6
  • m = mili = 10^-3
  • k = kilo= 10³
  • M = mega = 10⁶
  • G = giga = 10⁹
  • T = tera = 10¹²
• Flashlight Circuit
• Electrical Units
  • Current 1A = 6 x 10¹⁸ e-/sec = 1C/s
  • Voltage 1V = 1 J/C
  • Resistance 1 Ohm = 1 Js/C²
  • Power 1 W = 1 J/s

Analogies

• Reservoir
  Draw a picture of a reservoir with a pipe coming out of the bottom.
  Draw a sponge in the pipe.
  • Pressure ~ Voltage
  • Sponge Porosity ~ Resistance
  • Flow Rate ~ Current
• Marble in Oil
  Draw a container with a viscous fluid in it.
  Draw a marble falling through the fluid.
  • Weight of marble ~ Voltage
  • Viscosity ~ Resistance
  • Rate ~ Current

Electrical Symbols

• Voltage Sources
  • Circle with + and -
  • Thick bar over thin bar style
• Positive terminal
• Ground
• Resistors

Ohm's Law

• V = IR
• Defines resistors: linear relationship = resistor
• Insulators
  • Very large resistance (> 10 M Ohms)
  • Glass, Plastic, Air
• Conductors
  • Very small resistance (< 10 m Ohms)
  • Steel, Copper, Gold

Power

• True for any two terminal device
• Difference between dissipation & generation
• P = VI

Series Resistors

• R_eq = R₁ + R₂
• Example: P = 10V, R₁ = 2k, R₂ = 8k
• Example: Potentiometer Voltage Divider
  • Vo = Vs R₂/(R₁+R₂)
  • Ovens, Volume control, Tuners, Light Dimmers

Parallel Resistors

• Derive by example
• Kirchoff's Current Law: The sum of the currents entering a node is equal to the sum of the currents leaving the node.
• Req = R₁ R₂/(R₁ + R₂) = 1/(1/R₁ + 1/R₂)
• Show Req for many resistors in parallel
• When R₁=R₂, R_eq = R₁/2 = R₂/2
• For many resistors, R_eq = R/N where N is the number in parallel

Resistor Color Codes

• Blackberry Brandy Rots Our Young Guts, But Vodka Goes Well. Get Some Now.
• 20% have 3 colors
• 5% & 10% have 4 colors
• 1% & 2% have 5 colors