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Chapter 20

Chapter 20. Digital Circuits. Objectives. Explain the difference between analog and digital systems. Convert decimal numbers to their binary equivalents and binary numbers to their decimal equivalents. Name seven types of logic gates. Objectives.

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Chapter 20

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  1. Chapter 20 Digital Circuits

  2. Objectives • Explain the difference between analog and digital systems. • Convert decimal numbers to their binary equivalents and binary numbers to their decimal equivalents. • Name seven types of logic gates. Permission granted to reproduce for educational use only.

  3. Objectives • Explain the operation of various types of logic gates. • Use truth tables to determine the output of a logic gate. • Discuss two types of logic families. Permission granted to reproduce for educational use only.

  4. Objectives • Explain the digital encoders and decoders. • Explain analog-to-digital and digital-to-analog devices. • List three types of flip-flops and explain their truth tables. Permission granted to reproduce for educational use only.

  5. ICs • Include transistors, diodes, resistors, and capacitors • Major advantage is size • Linear circuits • Used as amplifiers and have variable outputs • Digital circuits • Used as switches and work in the on or off state Permission granted to reproduce for educational use only.

  6. Digital Fundamentals • Binary numbering system • Voltage logic levels • Bits, nibbles, and bytes Permission granted to reproduce for educational use only.

  7. Digital Advantages • Inexpensive, compared to analog systems • Easier information storage • Speed is greater than in analog systems • Compatibility with computers • Less effect from temperature changes Permission granted to reproduce for educational use only.

  8. Digital Characteristics • Capable of replacing analog systems • Cannot be distinguished from analog systems in most cases • Information is handled using switching circuits • Combination of logic gate and flip-flop circuits Permission granted to reproduce for educational use only.

  9. Binary Numbering System • Digital circuits act in on or off states • Comparable to a single-pole single-throw (SPST) switch • Switch in “on” position represents a 1 Permission granted to reproduce for educational use only.

  10. Basic Counting Rules • Digits must be recorded one after the other for each counting unit • When count exceeds total number of available digits, a second column begins • Decimal system’s first column ends at 9, and second column begins at 10 Permission granted to reproduce for educational use only.

  11. Binary System • 2 is comparable to decimal system’s 10 • 2 moves to second column, becomes a 0 or 1 Permission granted to reproduce for educational use only.

  12. Decimal to Binary Conversion Table Permission granted to reproduce for educational use only.

  13. Binary Numbers • Count binary numbers on your fingers • Number the fingers on your left hand as shown • Fingers pointing up are 1s, fingers folded down are 0s Permission granted to reproduce for educational use only.

  14. Large Binary Numbers and Addition Permission granted to reproduce for educational use only.

  15. Voltage Logic Levels in Digital Circuits • Type of logic circuitry or family affects operating voltages needed in a circuit • Valid logic high range • Valid logic low range • Invalid value range, or intermediate range Permission granted to reproduce for educational use only.

  16. Bits, Nibbles, and Bytes • Bit comes from joining binary and digit • Bit is smallest unit of information • Computer memory • Kilobytes • Megabytes • Gigabytes • Computer storage abilities are growing Permission granted to reproduce for educational use only.

  17. Review What is the primary difference between the decimal numbering system and the binary numbering system? The decimal system has numbers 0–9, and the binary system has 0 and 1 Permission granted to reproduce for educational use only.

  18. Review What is the smallest unit of information in binary code? A bit Permission granted to reproduce for educational use only.

  19. Logic Gates • AND gates • OR gates • NOT gates • NAND gates • NOR gates • XOR gates • XNOR gates Permission granted to reproduce for educational use only.

  20. AND Gates • Accepts high and low inputs (1 and 0) • High and low outputs • Output of 1 if all inputs are 1 • If only one gate is on, circuit will not work • Truth tables Permission granted to reproduce for educational use only.

  21. AND Gates (Cont.) Permission granted to reproduce for educational use only.

  22. AND Gates (Cont.) • Valid logic highs and lows Permission granted to reproduce for educational use only.

  23. OR Gates • Output signal of 1 if either or both inputs is 1 • When all inputs are 0, output is 0 • Acts similar to two switches in parallel Permission granted to reproduce for educational use only.

  24. OR Gates (Cont.) • Valid logic highs and lows Permission granted to reproduce for educational use only.

  25. NOT Gates • Used to invert polarity of input signal • Also called inverters • If input is 1, output is 0 • If input is 0, output is 1 Permission granted to reproduce for educational use only.

  26. NOT Gates (Cont.) • Valid logic highs and lows Permission granted to reproduce for educational use only.

  27. NAND Gates • Made of an AND gate and a NOT gate • Reverse of AND application • Also called NOT AND gates Permission granted to reproduce for educational use only.

  28. NAND Gates (Cont.) • Valid logic highs and lows Permission granted to reproduce for educational use only.

  29. NOR Gates • Opposite of OR gate • Made of OR and NOT gates • Used to test for any kind of input • No input will have output of 1 Permission granted to reproduce for educational use only.

  30. NOR Gates (Cont.) • Valid logic highs and lows Permission granted to reproduce for educational use only.

  31. XOR Gates • Also called exclusive OR gates • Provide high output if any, but not all, inputs are logic high • Provide low output if all inputs are logic high Permission granted to reproduce for educational use only.

  32. XOR Gates (Cont.) • Valid logic highs and lows Permission granted to reproduce for educational use only.

  33. XNOR Gates • Also called exclusive NOR gates • XOR gate with inverted output • High output only when all inputs are logic high or logic low Permission granted to reproduce for educational use only.

  34. Review Which gate has an output signal of 1 if either or both inputs is 1? OR gate Permission granted to reproduce for educational use only.

  35. Review Which gate provides high output if any, but not all, inputs are logic high, but provides a low output if all inputs are logic high? XOR gate Permission granted to reproduce for educational use only.

  36. Review Which gate is made of an AND and a NOT gate? NAND gate Permission granted to reproduce for educational use only.

  37. Review Which gate has an inverted output so it has a high output only when all inputs are logic high or logic low? XNOR Permission granted to reproduce for educational use only.

  38. Logic Families • Traits of one logic family must match traits of another family when many digital ICs are used in one device • Complementary metal-oxide semiconductor logic (CMOS) • Transistor-transistor logic (TTL) Permission granted to reproduce for educational use only.

  39. CMOS Logic • Circuits have good resistance to noise • Use FETs • Require small amounts of power • Can be damaged by static electricity • Worker and work surface must be grounded through high-resistance resistor Permission granted to reproduce for educational use only.

  40. TTL • Circuits work quickly • Function from 20 megahertz to 60 megahertz • Faster than CMOS ICs • Require high power dissipation and high current • Many gates can be placed in one TTL IC Permission granted to reproduce for educational use only.

  41. Review If many digital circuits are used in one device, how should logic families be treated? Traits of one logic family must match traits of another family Permission granted to reproduce for educational use only.

  42. Review Which of the two types of logic families can be easily damaged by static electricity? CMOS Permission granted to reproduce for educational use only.

  43. Digital Applications • Logic probes • Digital encoders and decoders • Digitized analog signals • Flip-flops • Counters Permission granted to reproduce for educational use only.

  44. Logic Probes • Indicate a high or low signal using LEDs • Connect to power supply of circuit being tested • Equipped with a slide switch to select the logic family • If both LEDs light, there is an invalid logic level voltage Permission granted to reproduce for educational use only.

  45. Digital Encoders and Decoders • Electronic systems translate binary system into decimal system • Analog-to-digital converters can change analog numbers to a digital number equivalent • Digital multimeter as example • Can convert electrical pulses into binary numbers Permission granted to reproduce for educational use only.

  46. Digitized Analog Signals • Digital signals representing sound waves or linear voltage • Analog-to-digital encoders are used Permission granted to reproduce for educational use only.

  47. Flip-Flops • Set-reset (R-S) flip-flops • J-K flip-flops • D flip-flops Permission granted to reproduce for educational use only.

  48. R-S Flip-Flops • When S is high, Q is high • Output represents last input setting if both inputs are low • Outputs are complementary • Clocked R-S flip-flops Permission granted to reproduce for educational use only.

  49. J-K Flip-Flops • Clock driven • Retain output status when two inputs are low • When both inputs are high, outputs toggle on and off Permission granted to reproduce for educational use only.

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