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Chapter 2 Algebraic Methods for the Analysis and Synthesis of Logic Circuits

Chapter 2 Algebraic Methods for the Analysis and Synthesis of Logic Circuits. Fundamentals of Boolean Algebra (1). Basic Postulates Postulate 1 (Definition) : A Boolean algebra is a closed algebraic system containing a set K of two or more elements and the two operators · and +.

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Chapter 2 Algebraic Methods for the Analysis and Synthesis of Logic Circuits

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  1. Chapter 2Algebraic Methods for the Analysis and Synthesis of Logic Circuits Chapter 2

  2. Fundamentals of Boolean Algebra (1) • Basic Postulates • Postulate 1 (Definition): A Boolean algebra is a closed algebraic system containing a set K of two or more elements and the two operators · and +. • Postulate 2 (Existence of 1 and 0 element): (a) a + 0 = a (identity for +),(b) a · 1 = a (identity for ·) • Postulate 3 (Commutativity): (a) a + b = b + a, (b) a · b = b · a • Postulate 4 (Associativity): (a) a + (b + c) = (a + b) + c (b) a·(b·c) = (a·b) ·c • Postulate 5 (Distributivity): (a) a + (b·c) = (a + b) ·(a + c) (b) a·(b + c) = a·b + a·c • Postulate 6 (Existence of complement): (a) (b) • Normally · is omitted. Chapter 2

  3. Fundamentals of Boolean Algebra (2) • Fundamental Theorems of Boolean Algebra • Theorem 1 (Idempotency): (a) a + a = a(b) aa = a • Theorem 2 (Null element): (a) a + 1 = 1 (b) a0 = 0 • Theorem 3 (Involution) • Properties of 0 and 1 elements (Table 2.1): OR AND Complement a + 0 = 0 a0 = 0 0' = 1 a + 1 = 1 a1 = a 1' = 0 Chapter 2

  4. Fundamentals of Boolean Algebra (3) • Theorem 4 (Absorption) (a) a + ab = a (b) a(a + b) = a • Examples: • (X + Y) + (X + Y)Z = X + Y [T4(a)] • AB'(AB' + B'C) = AB' [T4(b)] • Theorem 5 (a) a + a'b = a + b (b) a(a' + b) = ab • Examples: • B + AB'C'D = B + AC'D [T5(a)] • (X + Y)((X + Y)' + Z) = (X + Y)Z [T5(b)] Chapter 2

  5. Fundamentals of Boolean Algebra (4) • Theorem 6 (a) ab + ab' = a (b) (a + b)(a + b') = a • Examples: • ABC + AB'C = AC [T6(a)] • (W' + X' + Y' + Z')(W' + X' + Y' + Z)(W' + X' + Y + Z')(W' + X' + Y + Z) = (W' + X' + Y')(W' + X' + Y + Z')(W' + X' + Y + Z) [T6(b)] = (W' + X' + Y')(W' + X' + Y) [T6(b)] = (W' + X') [T6(b)] Chapter 2

  6. Fundamentals of Boolean Algebra (5) • Theorem 7 (a) ab + ab'c = ab + ac (b) (a + b)(a + b' + c) = (a + b)(a + c) • Examples: • wy' + wx'y + wxyz + wxz' = wy' + wx'y + wxy + wxz' [T7(a)] = wy' + wy + wxz'[T7(a)] = w + wxz' [T7(a)] = w [T7(a)] • (x'y' + z)(w + x'y' + z') = (x'y' + z)(w + x'y') [T7(b)] Chapter 2

  7. Fundamentals of Boolean Algebra (6) • Theorem 8 (DeMorgan's Theorem) (a) (a + b)' = a'b' (b) (ab)' = a' + b' • Generalized DeMorgan's Theorem (a) (a + b + … z)' = a'b' … z' (b) (ab … z)' = a' + b' + … z' • Examples: • (a + bc)' = (a + (bc))' = a'(bc)' [T8(a)] = a'(b' + c') [T8(b)] = a'b' + a'c'[P5(b)] • Note: (a + bc)' ¹ a'b' + c' Chapter 2

  8. Fundamentals of Boolean Algebra (7) • More Examples for DeMorgan's Theorem • (a(b + z(x + a')))' = a' + (b + z(x + a'))' [T8(b)] = a' + b' (z(x + a'))' [T8(a)] = a' + b' (z' + (x + a')') [T8(b)] = a' + b' (z' + x'(a')') [T8(a)] = a' + b' (z' + x'a) [T3] = a' + b' (z' + x') [T5(a)] • (a(b + c) + a'b)' = (ab + ac + a'b)' [P5(b)] = (b + ac)' [T6(a)] = b'(ac)' [T8(a)] = b'(a' + c') [T8(b)] Chapter 2

  9. Fundamentals of Boolean Algebra (8) • Theorem 9 (Consensus) (a) ab + a'c + bc = ab + a'c (b) (a + b)(a' + c)(b + c) = (a + b)(a' + c) • Examples: • AB + A'CD + BCD = AB + A'CD [T9(a)] • (a + b')(a' + c)(b' + c) = (a + b')(a' + c) [T9(b)] • ABC + A'D + B'D + CD = ABC + (A' + B')D + CD [P5(b)] = ABC + (AB)'D + CD [T8(b)] = ABC + (AB)'D [T9(a)] = ABC + (A' + B')D [T8(b)] = ABC + A'D + B'D [P5(b)] Chapter 2

  10. Switching Functions • Switching algebra: Boolean algebra with the set of elements K = {0, 1} • If there are n variables, we can define switching functions. • Sixteen functions of two variables (Table 2.3): • A switching function can be represented by a table as above, or by a switching expression as follows: • f0(A,B)= 0, f6(A,B) = AB' + A'B, f11(A,B) = AB + A'B + A'B' = A' + B, ... • Value of a function can be obtained by plugging in the values of all variables: The value of f6 when A = 1 and B = 0 is: = 0 + 1 = 1. Chapter 2

  11. Truth Tables (1) • Shows the value of a function for all possible input combinations. • Truth tables for OR, AND, and NOT (Table 2.4): Chapter 2

  12. Truth Tables (2) • Truth tables for f(A,B,C) = AB + A'C + AC' (Table 2.5) Chapter 2

  13. Algebraic Forms of Switching Functions (1) • Literal: A variable, complemented or uncomplemented. • Product term: A literal or literals ANDed together. • Sum term: A literal or literals ORed together. • SOP (Sum of Products): • ORing product terms • f(A, B, C) = ABC + A'C + B'C • POS (Product of Sums) • ANDing sum terms • f (A, B, C) = (A' + B' + C')(A + C')(B + C') Chapter 2

  14. Algebraic Forms of Switching Functions (2) • A minterm is a product term in which all the variables appear exactly once either complemented or uncomplemented. • Canonical Sum of Products (canonical SOP): • Represented as a sum of minterms only. • Example: f1(A,B,C) = A'BC' + ABC' + A'BC + ABC (2.1) • Minterms of three variables: Chapter 2

  15. Algebraic Forms of Switching Functions (3) • Compact form of canonical SOP form: f1(A,B,C) = m2 + m3 + m6 + m7 (2.2) • A further simplified form: f1(A,B,C) = Sm (2,3,6,7) (minterm list form) (2.3) • The order of variables in the functional notation is important. • Deriving truth table of f1(A,B,C) from minterm list: Chapter 2

  16. Algebraic Forms of Switching Functions (4) • Example: Given f(A,B,Q,Z) = A'B'Q'Z' + A'B'Q'Z + A'BQZ' + A'BQZ, express f(A,B,Q,Z) and f '(A,B,Q,Z) in minterm list form. f(A,B,Q,Z) = A'B'Q'Z' + A'B'Q'Z + A'BQZ' + A'BQZ = m0 + m1 + m6 + m7 = Sm(0, 1, 6, 7) f '(A,B,Q,Z) = m2 + m3 + m4 + m5 + m8 + m9 + m10 + m11 + m12 + m13 + m14 + m15 = Sm(2, 3, 4, 5, 8, 9, 10, 11, 12, 13, 14, 15) • (2.6) • AB + (AB)' = 1 and AB + A' + B'= 1, but AB + A'B'¹ 1. Chapter 2

  17. Algebraic Forms of Switching Functions (5) • A maxterm is a sum term in which all the variables appear exactly once either complemented or uncomplemented. • Canonical Product of Sums (canonical POS): • Represented as a product of maxterms only. • Example: f2(A,B,C) = (A+B+C)(A+B+C')(A'+B+C)(A'+B+C') (2.7) • Maxterms of three variables: Chapter 2

  18. Algebraic Forms of Switching Functions (6) • f2(A,B,C) = M0M1M4M5 (2.8) = PM(0,1,4,5) (maxterm list form) (2.9) • The truth table for f2(A,B,C): Chapter 2

  19. Algebraic Forms of Switching Functions (7) • Truth tables of f1(A,B,C) of Eq. (2.3) and f2(A,B,C) of Eq. (2.7) are identical. • Hence, f1(A,B,C) = Sm (2,3,6,7) = f2(A,B,C) = PM(0,1,4,5) (2.10) • Example: Givenf(A,B,C) = ( A+B+C')(A+B'+C')(A'+B+C')(A'+B'+C'), construct the truth table and express in both maxterm and minterm form. • f(A,B,C) = M1M3M5M7 = PM(1,3,5,7) = Sm (0,2,4,6) Chapter 2

  20. Algebraic Forms of Switching Functions (8) • Relationship between minterm mi and maxterm Mi: • For f(A,B,C), (m1)' = (A'B'C)' = A + B + C' = M1 • In general, (mi)' = Mi (2.11) (Mi)' = ((mi)')' = mi (2.12) Chapter 2

  21. Algebraic Forms of Switching Functions (9) • Example: Relationship between the maxterms for a function and its complement. • For f(A,B,C) = ( A+B+C')(A+B'+C')(A'+B+C')(A'+B'+C') • The truth table is: Chapter 2

  22. Algebraic Forms of Switching Functions (10) • From the truth table f '(A,B,C) = PM(0,2,4,6) and f(A,B,C) = PM(1,3,5,7) • Since f(A,B,C) × f '(A,B,C) = 0, (M0M2M4M6)(M1M3M5M7) = 0 or • In general, (2.13) • Another observation from the truth table: f(A,B,C) = Sm (0,2,4,6) = PM(1,3,5,7) f '(A,B,C) = Sm (1,3,5,7) = PM(0,2,4,6) Chapter 2

  23. Derivation of Canonical Forms (1) • Derive canonical POS or SOP using switching algebra. • Theorem 10. Shannon's expansion theorem (a). f(x1, x2, …, xn) = x1f(1, x2, …, xn) + (x1)' f(0, x2, …, xn) (b). f(x1, x2, …, xn) = [x1 + f(0, x2, …, xn)] [(x1)' + f(1, x2, …, xn)] • Example: f(A,B,C) = AB + AC' + A'C • f(A,B,C) = AB + AC' + A'C = A f(1,B,C) + A' f(0,B,C) = A(1×B + 1×C' + 1'×C) + A'(0×B + 0×C' + 0'×C) = A(B + C') + A'C • f(A,B,C) = A(B + C') + A'C = B[A(1+C') + A'C] + B'[A(0 + C') + A'C] = B[A + A'C] + B'[AC' + A'C] = AB + A'BC + AB'C' + A'B'C • f(A,B,C) = AB + A'BC + AB'C' + A'B'C = C[AB + A'B×1 + AB'×1' + A'B'×1] + C'[AB + A'B×0 + AB'×0' + A'B'×0] = ABC + A'BC + A'B'C + ABC' + AB'C' Chapter 2

  24. Derivation of Canonical Forms (2) • Alternative: Use Theorem 6 to add missing literals. • Example: f(A,B,C) = AB + AC' + A'C to canonical SOP form. • AB = ABC' + ABC = m6 + m7 • AC' = AB'C' + ABC' = m4 + m6 • A'C = A'B'C + A'BC = m1 + m3 • Therefore, f(A,B,C) = (m6 + m7) + (m4 + m6) + (m1 + m3) = m(1, 3, 4, 6, 7) • Example: f(A,B,C) = A(A + C') to canonical POS form. • A = (A+B')(A+B) = (A+B'+C')(A+B'+C)(A+B+C')(A+B+C) = M3M2M1M0 • (A+C')= (A+B'+C')(A+B+C') = M3M1 • Therefore, f(A,B,C) = (M3M2M1M0)(M3M1) = M(0, 1, 2, 3) Chapter 2

  25. Incompletely Specified Functions • A switching function may be incompletely specified. • Some minterms are omitted, which are called don't-care minterms. • Don't cares arise in two ways: • Certain input combinations never occur. • Output is required to be 1 or 0 only for certain combinations. • Don't care minterms: di Don't care maxterms: Di • Example: f(A,B,C) has minterms m0, m3, and m7 and don't-cares d4 and d5. • Minterm list is: f(A,B,C) = m(0,3,7) + d(4,5) • Maxterm list is: f(A,B,C) = M(1,2,6)·D(4,5) • f '(A,B,C) = m(1,2,6) + d(4,5) = M(0,3,7)·D(4,5) • f (A,B,C)= A'B'C' + A'BC + ABC + d(AB'C' + AB'C) = B'C' + BC (use d4 and omit d5) Chapter 2

  26. Electronic Logic Gates (1) • Electrical Signals and Logic Values • A signal that is set to logic 1 is said to be asserted, active, or true. • An active-high signal is asserted when it is high (positive logic). • An active-low signal is asserted when it is low (negative logic). Chapter 2

  27. Electronic Logic Gates (2) Chapter 2

  28. Electronic Logic Gates (3) Chapter 2

  29. Electronic Logic Gates (4) Chapter 2

  30. Electronic Logic Gates (5) Chapter 2

  31. Basic Functional Components (1) • AND (a) AND logic function. (b) Electronic AND gate. (c) Standard symbol. (d) IEEE block symbol. Chapter 2

  32. Basic Functional Components (2) • OR (a) OR logic function. (b) Electronic OR gate. (c) Standard symbol. (d) IEEE block symbol. Chapter 2

  33. Basic Functional Components (3) • Meaning of the designation  1 in IEEE symbol: Chapter 2

  34. Basic Functional Components (4) • NOT (a) NOT logic function. (b) Electronic NOT gate. (c) Standard symbol. (d) IEEE block symbol. Chapter 2

  35. Basic Functional Components (5) • Positive Versus Negative Logic Chapter 2

  36. Basic Functional Components (6) • AND Gate Usage in Negative Logic • (a) AND gate truth table (L = 1, H = 0) • (b) Alternate AND gate symbol (in negative logic) • (c) Preferred usage • (d) Improper usage • y = a·b = (2.14) • (2.15) Chapter 2

  37. Basic Functional Components (7) • OR Gate Usage in Negative Logic • (a) OR gate truth table(L = 1, H = 0) • (b) Alternate OR gate symbol (in negative logic) • (c) Preferred usage • (d) Improper usage • (2.16) • (2.17) Chapter 2

  38. Basic Functional Components (8) • Example 2.32: Building smoke alarm system • Components:two smoke detectors, a sprinkler, and an automatic telephone dialer • Behavior: • Sprinkler is activated if either smoke detector detects smoke. • When both smoke detector detect smoke, fire department is called. • Signals: • : Active-low outputs from two smoke detectors. • : Active-low input to the sprinkler • : Active-low input to the telephone dialer. • Logic equations • (2.18) • (2.19) Chapter 2

  39. Basic Functional Components (9) • Logic diagram of the smoke alarm system Chapter 2

  40. Basic Functional Components (10) • NAND • (a) NAND logic function • (b) Electronic NAND gate • (c) Standard symbol • (d) IEEE block symbol Chapter 2

  41. Basic Functional Components (10) • Matching signal polarity to NAND gate inputs/outputs • (a) Preferred usage (b) Improper usage • Additional properties of NAND gate: • Hence, NAND gate may be used to implement all three elementary operators. Chapter 2

  42. Basic Functional Components (11) • AND, OR, and NOT gates constructed exclusively from NAND gates Chapter 2

  43. Basic Functional Components (12) • NOR • (a) NAND logic function • (b) Electronic NAND gate • (c) Standard symbol • (d) IEEE block symbol Chapter 2

  44. Basic Functional Components (13) • Matching signal polarity to NOR gate inputs/outputs • (a) Preferred usage (b) Improper usage • Additional properties of NAND gate: • Hence, NAND gate may be used to implement all three elementary operators. Chapter 2

  45. Basic Functional Components (14) • AND, OR, and NOT gates constructed exclusively from NOR gates. Chapter 2

  46. Basic Functional Components (15) • Exclusive-OR (XOR) • fXOR(a, b) = a  b = (2.24) (a) XOR logic function (b) Electronic XOR gate (c) Standard symbol (d) IEEE block symbol Chapter 2

  47. Basic Functional Components (16) • POS of XOR a  b [P2(a), P6(b)] [P5(b)] [P5(b)] • Some other useful relationships • a a = 0 (2.25) • a  = 1 (2.26) • a  0 = a (2.27) • a  1 = (2.28) • (2.29) • a  b = b  a (2.30) • a  (b  c) = (a  b)  c (2.31) Chapter 2

  48. Basic Functional Components (17) • Output of XOR gate is asserted when the mathematical sum of inputs is one: • The output of XOR is the modulo-2 sum of its inputs. Chapter 2

  49. Basic Functional Components (18) • Exclusive-NOR (XNOR) • fXNOR(a, b) = ab (2.32) • (a) XNOR logic function • (b) Electronic XNOR gate • (c) Standard symbol • (d) IEEE block symbol Chapter 2

  50. Basic Functional Components (19) • SOP and POS of XNOR ab [P2] [T8(a)] [T8(b)] [P5(b)] [P6(b), P2(a)] • = ab Chapter 2

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