218L6S09 - 2/12/09 ESE218 Spring 2009 Lecture 6 1 ESE218...

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Unformatted text preview: 2/12/09 ESE218 Spring 2009 Lecture 6 1 ESE218 Lecture 6. Two-level implementations. Standard forms. Outline Implementations of algebraic expressions AND-OR vs NAND-NAND OR-AND vs NOR-NOR Open-drain, three-state and wired logic AOI and OAI Standard forms SOP and POS, form conversion Canonical standard forms minterms, sum of minterms Maxterms, products of maxterms form conversion Summary 2/12/09 ESE218 Spring 2009 Lecture 6 2 Implementations of algebraic expressions Straightforward implementations AND-OR for SOP form OR-AND for POS form Better implementations NAND-NAND as equivalent to AND-OR NOR-NOR as equivalent to OR-AND THE BEST implementations AND-OR-INVERT OR-AND-INVERT Circuits with open drain, wired logic Propagation delay Large Small 2/12/09 ESE218 Spring 2009 Lecture 6 3 NAND + inverter = AND AND gate is a two-stage circuit, it contains NAND gate and an inverter. The latter results in longer propagation delay compared to that in a single NAND gate a R +V DD b c=(ab) NAND R AND R +V DD a b ab (ab) NAND + Inverter 2/12/09 ESE218 Spring 2009 Lecture 6 4 AND-OR implementation SOP: F(A,B,C,D) = AB + CD A Too many inverters longer propagation delay B C D 5 7408 1 2 3 7408 1 2 3 F AND =NAND+INVERTER OR = NOR+INVERTER Let us exclude the unnecessary inverters using properties of Boolean algebra! 2/12/09 ESE218 Spring 2009 Lecture 6 5 NAND-NAND implementation...
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218L6S09 - 2/12/09 ESE218 Spring 2009 Lecture 6 1 ESE218...

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