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Referred Books/Source

Analog and digital electronics 18CS33 Prof. Anand S. Hiremath, Dept. of CSE, BLDEA’s CET, Vijayapur http://ashiremath.wordpress.com ashiremath@bldeacet.ac.in. Referred Books/Source. Charles H Roth and Larry L Kinney, Analog and Digital Electronics, Cengage Learning,2019

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Referred Books/Source

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  1. Analog and digital electronics18CS33Prof. Anand S. Hiremath,Dept. of CSE, BLDEA’s CET, Vijayapurhttp://ashiremath.wordpress.comashiremath@bldeacet.ac.in

  2. Referred Books/Source • Charles H Roth and Larry L Kinney, Analog and Digital Electronics, Cengage Learning,2019 • Charles H Roth and Larry L Kinney, Fundamental of Logic Design, Cengage Learning, 2017. • Donald P Leach, Albert Paul Malvino & GoutamSaha: Digital Principles and Applications, 7th Edition, Tata McGraw Hill, 2015

  3. Module-2 Karnaughmaps & Quine-McCluskyMethod

  4. Basic Gates-1 • A logic gate is a digital circuit with 1 or more input voltages but only 1 output voltage. • Logic gates are the fundamental building blocks of digital systems. • By connecting the different gates in different ways, we can build circuits that perform arithmetic and other functions associated with the human brain. • Because the circuits simulate mental processes, gates are often called logic circuits. NOT, OR & AND gates are the basic types of gates. • The inter-connection of gates to perform a variety of logical operations is called logic design. • The operation of a logic gate can be easily understood with the help of "truth table". • A truth table lists all possible combinations of inputs and the corresponding outputs.

  5. Basic Gates-2 • NOT GATE (INVERTER) • It is a gate with only 1 input and a complemented output.

  6. Basic Gates-3 • AND GATE • This is a gate with 2 or more inputs. • The output is HIGH only when all inputs are HIGH.

  7. Basic Gates-4

  8. Basic Gates-5 • OR GATE • This is a gate with 2 or more inputs. • The output is HIGH when any input is HIGH.

  9. Basic Gates-6

  10. Basic Gates-9 • NOR GATE • This represents an OR gate followed by an inverter.

  11. Basic Gates-10 • Universality of NOR Gate

  12. Basic Gates-11 • NAND GATE • This represents an AND gate followed by an inverter.

  13. Basic Gates-12 • Universality of NAND Gate

  14. EXCLUSIVE-OR GATES-1 • The exclusive-OR gate has a high output only when an odd number of inputs is high. • OR • Y = A⨁B

  15. EXCLUSIVE-OR GATES-2

  16. A Y B EXCLUSIVE-OR GATES-2 • EX-NOR Gate • Truth Table • Y = A⨀B • OR • or

  17. Introduction • Each gate input is labelled with a variable. • Each appearance of a variable or its complement in an expression will be referred to as a literal. • The following expression, which has three variables, has 10 literals • ab′c + a′b + a′bc′ + b′c′ • A truth table (also called a table of combinations) specifies the values of a Boolean expression for every possible combination of values of the variables in the expression.

  18. Introduction • An expression is said to be in sum-of-products (SOP)form when all products are the products of single variables. • E.g. AB′ + CD′E + AC′E′ • A sum-of-products expression can be realized using one or more AND gates feeding a single OR gate at the circuit output. • An expression is in product-of-sums (POS) form when all sums are the sums of single variables. • E.g. (A + B′)(C + D′ + E)(A + C′ + E′) • A product-of-sumsexpression can be realized using one or more OR gates feeding a single AND gate at the circuit output.

  19. Introduction

  20. Introduction • Redundant Terms: The Term not or no longer needed or useful. • (A + BC)(A + D + E) • = A + AD + AE + ABC + BCD + BCE • = A(1 + D + E + BC) + BCD + BCE • = A + BCD + BCE

  21. Introduction • The Consensus Theorem • Useful in simplifying Boolean expressions. • The consensus theorem can be used to eliminate redundant terms from Boolean expressions. • E.g. XY + X′Z + YZ, • the term YZ is redundant and can be eliminated to form the equivalent expression XY + X′Z. The term that was eliminated is referred to as the consensus term. • Given a pair of terms for which a variable appears in one term and the complement of that variable in another, the consensus term is formed by multiplying the two original terms together, leaving out the selected variable and its complement. • E.g. • The consensus of ab and a′c is bc; • The consensus of abd and b′de′ is (ad)(de′) = ade′. • The consensus of terms ab′d and a′bd′ is 0.

  22. SUM-Of-PRODUCTS (SOP)Method-1 • Possible ways to AND two or more input signals that are in complement and uncomplement form. • A SOP expression is two or more AND functions ORed together.

  23. SUM-Of-PRODUCTS (SOP)Method-2 • ANDing two variables and their complements

  24. SUM-Of-PRODUCTS (SOP)Method-3 • The fundamental products are also called minterms. • Products are represented by m0, m1, m2 and m3 respectively. The suffix i of mi comes from decimal equivalent of binary values that makes corresponding product term high.

  25. SUM-Of-PRODUCTS (SOP)Method-4 • Example: • Fundamental Products for Three Inputs

  26. SUM-Of-PRODUCTS (SOP)Method-5 • The above three variable minterms can alternatively be represented by mo, m1, m2, m3, m4, m5, m6, and m7 respectively. Note that, for n variable problem there can be 2n number of minterms. • The fundamental products by listing each one next to the input condition that results in a high output. • For instance, when A = 1, B = 0 and C = 0, the fundamental product results in an output of

  27. Sum-of-Products Equation-1 • Sum-of-Products Equation • The Sum-of-products solution, for given a truth table shown below. • Write down the fundamental product for each output 1 in the truth table. For example, the first output 1 appears for an input of A = 0, B = 1, and C = 1. The corresponding fundamental product is .

  28. Sum-of-Products Equation-2 • To get the sum-of-products equation, all you have to do is OR the fundamental products • Alternate representation

  29. Sum-of-Products Equation-3 • where '∑:' symbolizes summation or logical OR operation that is performed on corresponding minterm’sand Y = F (A, B, C) means Y is a function of three Boolean variables A, B and C. This kind of representation of a truth table is also known as canonical sum form.

  30. Logic Circuit

  31. Lab Experiment • Design and implement Half adder, Full Adder, Half Subtractor, Full Subtractor using basic gates. • Half Adder: • Truth Table for Half Adder • Logic Expression

  32. PRODUCT-Of-SUMS METHOD-1 • Given a truth table, identify the fundamental sums needed for a logic design. Then by ANDing these sums, will get the product-of-sums equation corresponding to the truth table. • But, in the sum-of-products method, the fundamental product produces an output l for the corresponding input condition. • But with the product of- sums method, the fundamental sum produces an output 0 for the corresponding input condition.

  33. PRODUCT-Of-SUMS METHOD-2 • Converting a Truth Table to an Equation

  34. PRODUCT-Of-SUMS METHOD-3 • Logic Circuit

  35. PRODUCT-Of-SUMS METHOD-4 • Conversion between SOP and POS • SOP and POS occupy complementary locations in a truth table. • Identifying complementary locations, • Changing mintermto maxtermor reverse, and • Changing summation by product or reverse.

  36. Conversion between SOP and POS • Mapping between canonical forms • Mintermto maxterm conversion • use maxterms whose indices do not appear in minterm expansion • e.g. F(A,B,C) = ∑m(1,3,5,6,7) = ∏M(0,2,4) • Maxtermto minterm conversion • use minterms whose indices do not appear in maxterm expansion • e.g. F(A,B,C) = ∏ M(0,2,4) = ∑ m(1,3,5,6,7) • Mintermexpansion of F to minterm expansion of • use minterms whose indices do not appear • e.g., F(A,B,C) = ∑ m(1,3,5,6,7) (A,B,C) = ∑ m(0,2,4) • Maxtermexpansion of F to maxterm expansion of • use maxterms whose indices do not appear • e.g., F(A,B,C) = ∏ M(0,2,4) ’(A,B,C) = ∏ M(1,3,5,6,7)

  37. DON'T-CARE CONDITIONS-1 • In digital systems, certain input conditions never occur during normal operation; therefore, the corresponding output never appears. Since the output never appears, it is indicated by an X in the truth table. • The X is called a don 't-care condition. Whenever you see an X in a truth table, you can let it equal either 0 or 1, whichever produces a simpler logic circuit.

  38. DON'T-CARE CONDITIONS-2 • Truth Table with Don’t-Cares • In Minterm form • F =Σ m(0, 3, 7) +Σ d(1, 6) • In Maxterm form • F =Π M(2, 4, 5)· Π D(1, 6)

  39. DON'T-CARE CONDITIONS-2 • Truth Table with Don't-Care Conditions • Y=F(A,B,C,D) = ∑m (9) + d(10,11,12,13,14,15)

  40. Problems • Design a logic circuit that has three inputs, A, B, and C, and whose output will be HIGH only when a majority of the inputs are HIGH.

  41. Karnaugh Maps • Switching functions can generally be simplified by using the algebraic techniques. • However, two problems arise when algebraic procedures are used: • 1. The procedures are difficult to apply in a systematic way. • 2. It is difficult to tell when you have arrived at a minimum solution. • The Karnaugh map method and the Quine-McCluskey procedure used to overcome these difficulties by providing systematic methods for simplifying switching functions. • The Karnaugh map is useful tool for simplifying and manipulating switching functions of three or four variables (Literals).

  42. Karnaugh MapsMinimum Forms of Switching Functions • When a function is realized using AND and OR gates, the cost of realizing the function is directly related to the number of gates and gate inputs used. • The Karnaugh map techniques developed that lead directly to minimum cost two-level circuits composed of AND and OR gates. • An expression consisting of a sum of product terms corresponds directly to a two-level circuit composed of a group of AND gates feeding a single OR gate. • Similarly, a product-of-sums expression corresponds to a two-level circuit composed of OR gates feeding a single AND gate. • Therefore, to find minimum cost two-level AND-OR gate circuits, we must find minimum expressions in sum-of-products or product-of-sums form.

  43. Karnaugh MapsMinimum Forms of Switching Functions • A minimum sum-of-products expression for a function is defined as a sum of product terms which • (a) has a minimum number of terms and • (b) of all those e xpressions which have the same minimum number of terms, has a minimum number of literals. • The minimum sum of products corresponds directly to a minimum two-level gate circuit which has • (a) a minimum number of gates and • (b) a minimum number of gate inputs. • Unlike the minterm expansion for a function, the minimum sum of products is not necessarily unique; that is, a given function may have two different minimum sum-of-products forms, each with the same number of terms and the same number of literals.

  44. Karnaugh MapsMinimum Forms of Switching Functions • Given a minterm expansion, the minimum sum-of-products form can often be obtained by the following procedure: • 1. Combine terms by using the uniting theorem XY′ + XY = X. Do this repeatedly to eliminate as many literals as possible. A given term may be used more than once because X + X = X. • 2. Eliminate redundant terms by using the consensus theorem or other theorems. • Note: Unfortunately, the result of this procedure may depend on the order in which terms are combined or eliminated so that the final expression obtained is not necessarily minimum.

  45. Karnaugh MapsMinimum Forms of Switching Functions • Find a minimum sum-of-products expression for F(a, b, c) = m Σ (0, 1, 2, 5, 6, 7)

  46. Karnaugh MapsMinimum Forms of Switching Functions • A minimum product-of-sums expression for a function is defined as a product of sum terms which • (a) has a minimum number of terms, and • (b) of all those expressions which have the same number of terms, has a minimum number of literals. • Unlike the maxterm expansion, the minimum product-of-sums form of a function is not necessarily unique. • Minimum product of sums can often be obtained by uniting theorem (X + Y)(X + Y′) = X is

  47. Karnaugh MapsMinimum Forms of Switching Functions • Mintermsand products are represented in algebraic notation or binary notation. • The first four-variable example below illustrates this for minterms and the second for products containing three literals. The dash indicates a missing variable. • ab′cd′ + ab′cd = ab′c • 1 0 1 0 + 1 0 1 1 = 101– • ab′c + abc = ac • 1 0 1– + 111– = 1–1– • Note that minterms only combine if they differ in one variable, and products only combine if they have dashes in the same position (same missing variables) and differ in one other variable.

  48. Karnaugh MapsTwo- and Three-Variable KarnaughMaps

  49. Karnaugh MapsTwo- and Three-Variable KarnaughMaps • Mintermsin adjacent squares of the map can be combined since they differ in only one variable. • Thus, A′B′ and A′B combine to form A′, and this is indicated by looping (Grouping) the corresponding 1’s on the map in Figure

  50. Karnaugh MapsTwo- and Three-Variable Karnaugh Maps • Two-Variable Maps • Example: Y =F(A,B)= ∑m(2,3)

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