Week 1 Part 3

Week 1 Part 3 - EECE 201 Project Integrated Program Module...

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1 SG EECE 201, Module 2, Set 3 EECE 201 Project Integrated Program Module 2, Fall 2009 Set 3: Implementation Technology Sathish Gopalakrishnan Department of Electrical and Computer Engineering University of British Columbia sathish@ece.ubc.ca
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2 SG EECE 201, Module 2, Set 3 Representation of Logic Values Logic variables can be represented as signals in electronic circuits. These values can be represented either as voltage or current levels. In a positive logic system logic value 0 is represented by low voltage levels and logic value 1 is represented by high voltage levels. (Could you guess how logic values are represented in negative logic system?) In positive logic systems logic values “0” and “1” are simply referred to as “low” and “high”. A common approach for representing binary logic values is to define threshold voltages.
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3 SG EECE 201, Module 2, Set 3 Representing Logic Values as Voltage Levels Logic values in a positive logic system
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4 SG EECE 201, Module 2, Set 3 Transistors as Switches The most popular type of transistors for implementing a simple switch is MOS transistor. There are two types of MOS transistors: NMOS and PMOS NMOS: Drain Source x = "low" x = "high" (a) A simple switch controlled by the input x V D V S (b) NMOS transistor Gate (c) Simplifed symbol For an NMOS transistor V G Substrate (Body)
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5 SG EECE 201, Module 2, Set 3 Transistors as Switches PMOS: Gate x = "high" x = "low" (a) A switch with the opposite behavior of Figure 3.2 a V G V D V S (b) PMOS transistor (c) Simpli±ed symbol for a PMOS transistor V DD Drain Source Substrate (Body)
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6 SG EECE 201, Module 2, Set 3 Typical Use of MOS Transistors in Logic Circuits An NMOS transistor is turned on when its gate is “high”, while a PMOS transistor is turned on when its gate is “low”. In the following circuits, when the NMOS transistor is on its drain is pulled down to ground and when the PMOS transistor is on its drain is pulled up to V DD . Because of the way transistors operate, an NMOS cannot be used to pull its drain up to V DD . (a) NMOS transistor V G V D V S = 0 V V S = V DD V D V G Closed switch when V G = V DD V D = 0 V Open switch when V G = 0 V V D Open switch when V G = V DD V D V DD Closed switch when V G = 0 V V D = V DD V DD (b) PMOS transistor
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7 SG EECE 201, Module 2, Set 3 MOS Logic Gates MOS transistor as building blocks of logic gates became popular in the 1970s. The first generation of logic gates using MOS transistors
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Week 1 Part 3 - EECE 201 Project Integrated Program Module...

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