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EET 1131 Unit 2 Digital Signals and Switches

EET 1131 Unit 2 Digital Signals and Switches. Read Kleitz, Sections 2-1 to 2-5, and Section 2-12. Skim the rest of Chapter 2. Homework #2 and Lab #2 due next week. Quiz next week. Digital Signal.

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EET 1131 Unit 2 Digital Signals and Switches

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  1. EET 1131 Unit 2Digital Signals and Switches • Read Kleitz, Sections 2-1 to 2-5, and Section 2-12. Skim the rest of Chapter 2. • Homework #2 and Lab #2 due next week. • Quiz next week.

  2. Digital Signal • In digital circuits, the logic level at any point usually changes as time passes. This changing level is called a digital signal (or digital waveform).

  3. Graph of a Digital Signal • We can describe a digital signal by graphing the voltage (or logic level) versus time.

  4. Oscilloscope • For slow-changing signals, you could graph a digital signal by hand, using a logic probe and a wristwatch. • But usually we use an oscilloscope to do this work for us.

  5. Periodic Digital Signal • A periodic digital signal is one that repeats itself at regular intervals. • Which one of these signals is periodic?

  6. Cycle • In a periodic signal, each repetition is called a cycle. • How many cycles are shown in the diagram below?

  7. Period • The time required for one cycle is called the signal’s period. • The symbol for period is tp. (Some books use T.) • Period is measured in seconds, abbreviated s. • Example: If a signal repeats itself every 3 seconds, we’d write tp = 3 s

  8. Frequency • A signal’s frequencyis the number of cycles that occur in one second. • The symbol for frequency is f. • Frequency is measured in hertz, abbreviated Hz. • Some old-timers say “cycles per second” instead of “hertz.” • Example: If a signal repeats itself 20 times every second, we’d write f = 20 Hz

  9. Period and Frequency • Period and frequency are the reciprocal of each other: f = 1 / tp tp = 1 / f • What are the period and frequency of this signal?

  10. Large and Small Numbers • Technicians often deal with very large or very small numbers. • Example: a system’s clock signal might have a frequency of 750,000 Hz and a period of 0.00000133 s. • It’s not convenient to write or discuss numbers using so many zeroes. Instead we use engineering prefixes, which are abbreviations for certain powers of 10.

  11. Engineering Prefix Game • You must memorize these prefixes. • To practice, play the Metric Prefix matching game on my Games page.

  12. Using Engineering Prefixes • Whenever you have a number that’s greater than 1000 or less than 1, you should use these prefixes. • Examples: • Instead of writing 750,000 Hz, write 750 kHz (pronounced “750 kilohertz”). • Instead of writing 0.00000133 s,write 1.33 s (pronounced “1.33 microseconds”).

  13. Calculator’s Exponent Key • Scientific calculators have an exponent key (usually labeled EE, EXP, or E) that lets you easily enter numbers with engineering prefixes. • Examples: • To enter 750 k, press 750 EE 3. • To enter 1.33 , press 1.33 EE −6.

  14. Calculator Modes • Most scientific calculators also have an engineering mode, which forces the answer always to be displayed with one of the engineering powers of 10. • Learn how to use this feature of your calculator. It will save you from making mistakes.

  15. Function Generator • To produce a periodic digital signal, you could use a switch that you flip up and down by hand at regular intervals. • But usually we use a function generator to do this work for us.

  16. Trainer Function Generator Regular Output, controlled by all four knobs. You’ll use this in other courses. No matter which one of these you use, you must also use the GROUND connection. TTL Mode Output, controlled by the FREQUENCY and RANGE knobs. In this course we’ll always use this one.

  17. Digital Waveforms Digital waveforms change between the LOW and HIGH levels. A positive going pulse is one that goes from a normally LOW logic level to a HIGH level and then back again. Digital waveforms are made up of a series of pulses.

  18. Timing Diagrams A timing diagram(or waveform diagram) is used to show the relationship between two or more digital waveforms.

  19. Serial and Parallel Data Data can be transmitted by either serial transfer or parallel transfer.

  20. Serial Transmission • Uses a single electrical conductor for data, so it’s inexpensive. • Slow, since only one bit for each clock period. • Used for telephone lines, computer-to-computer networks. • Computer COM ports and USB ports are used for serial communications. • Ethernet plug-in cards are for serial networking.

  21. Serial Representation of a Binary Number • A serial representation of the binary number 01101100 is illustrated below. • Note that only one bit is transmitted per clock period.

  22. Parallel Transmission • Separate electrical conductor for each bit, so more expensive than serial. • Very fast • Inside a computer • Data bus • External Devices • Centronics printer interface (LPT1) • SCSI (Small Computer Systems Interface)

  23. Serial versus Parallel Transmission • Question 1: How long will it take to transmit an 8-bit binary string using serial transmission if the clock frequency is 25 MHz? • Question 2: How long will it take to transmit an 8-bit binary string using parallel transmission if the clock frequency is 25 MHz?

  24. Ports on a Typical Laptop Computer RS-232(Serial) USB(Serial) PS/2 Mouse (Serial) IEEE 1394(Serial) Printer (Parallel) VGA (Analog video)

  25. Ports on a Fluke 45 DMM IEEE 488 (“GPIB”) option not installed (Parallel) RS-232(Serial)

  26. Ports on a Tektronix TDS2014 RS-232(Serial) Printer (Parallel) IEEE 488 (“GPIB”) (Parallel)

  27. Switches • A digital circuit is basically a combination of a huge number of switches. • Each switch is either on or off at any given time. • Unlike manual switches that require a person to switch them, we need automatic switches that can be turned on or off by the voltage level (HIGH or LOW) present at the switch’s control input.

  28. Electromechanical Relays • Before the invention of semiconductor devices in the mid-1900s, the electromechnical relay was the main type of automatic switch. • Still used in industrial applications, where large currents are involved.

  29. Electronic Switches • Relays are slow, large, and expensive compared to modern electronic switches (diodes and transistors). • In past decades, some digital electronics used diodes as switches, but today almost all digital electronics is based on using transistors as switches.

  30. Two Kinds of Transistors • In Electronic Devices & Circuits (EET 2201) you’ll study two major classes of transistors: • Bipolar Junction Transistors (BJTs) • Metal-Oxide Semiconductor Field Effect Transistor (MOSFETs)

  31. Logic Families • Two major logic families: • TTL (Transistor-Transistor Logic) based on bipolar junction transistors • CMOS (Complementary Metal Oxide Semiconductor) based on MOSFETs • Within each family are several subfamilies; we’ll study these in Chapter 9. • Originally, TTL chips were fast but used lots of power, and CMOS chips used little power but were slow. • CMOS chips are sensitive to static discharge, and must be handled carefully.

  32. 7400 Series and 4000 Series • A popular series of TTL chips is the 7400 series that you’ll use in Sinclair’s digital courses: Wikipedia's list • A popular series of CMOS chips is the 4000 series: Wikipedia's list

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