MIT6_012S09_lec11

# MIT6_012S09_lec11 - Lecture 11 Digital Circuits(I THE...

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Lecture 11 Digital Circuits (I) THE INVERTER Outline Introduction to digital circuits –The inverter • NMOS inverter with resistor pull-up Reading Assignment: Howe and Sodini; Chapter 5, Sections 5.1-5.3 1 6.012 Spring 2009 Lecture 11

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1. Introduction to digital circuits: the inverter In digital circuits, digitally-encoded information is represented by means of two distinct voltage ranges: V V MAX V OH V OL logic 0 V MIN logic 1 undefined � region The Static De fi nition Logic 0: V MIN ± V ± V OL Logic 1: V OH ± V ± V MAX Unde fi ned logic value: V OL ± V ± V OH Logic operations are performed using logic gates . Simplest logic operation of all: inversion ² inverter 2 6.012 Spring 2009 Lecture 11
Ideal inverter IN OUT 1 OUT=IN 0 1 IN 0 Circuit representation and ideal transfer function: V OUT v + V + V OUT =V IN V + + + 2 V OUT V IN - - 0 0 V M = V + V + V IN 2 De fi ne switching point or logic threshold : V M ± input voltage for which V OUT = V IN – For 0 ± V IN < V M ² V OUT = V + – For V M < V IN ± V + ² V OUT = 0 Ideal inverter returns well de fi ned logical outputs (0 or V + ) even in the presence of considerable noise in V IN (from voltage spikes, crosstalk, etc.) ² signal is regenerated ! 6.012 Spring 2009 Lecture 11 3

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“Real” inverter Logic 0: V MIN ± output voltage for which V IN = V + V OL ± smallest output voltage where slope = -1 Logic 1: V OH ± largest output voltage where slope = -1 V MAX ± output voltage for which V IN = 0 In a real inverter, valid logic levels de fi
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