L2+Basic+Logic+Gates - Switches Electronic switches are the...

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1 Ve270 Introduction to Logic Design 1 Lecture 2 Basic Logic Gates Ve270 Introduction to Logic Design 2 Switches Electronic switches are the basis of binary digital circuits – Electrical terminology Voltage : Difference in electric potential between two points – Analogous to water pressure Current : Flow of charged particles – Analogous to water flow Resistance : Tendency of wire to resist current flow – Analogous to water pipe diameter • V = I * R (Ohm’s Law) 4.5 A 2 ohms 9V 0V 9V + Ve270 Introduction to Logic Design 3 Switches A switch has three parts – Source input, output • Current wants to flow from source input to output – Control input • Voltage that controls whether that current can flow The amazing shrinking switch – 1930s: Relays – 1940s: Vacuum tubes – 1950s: Discrete transistor – 1960s: Integrated circuits (ICs) • Initially just a few transistors on IC • Then tens, hundreds, thousands. .. “off” “on” output source input output source input control input control input relay vacuum tube discrete transistor IC a Ve270 Introduction to Logic Design 4 Moore’s Law IC capacity doubling about every 18 months for several decades – Known as “Moore’s Law” after Gordon Moore, co-founder of Intel • Predicted in 1965 predicted that components per IC would double roughly every 18 months or so – For a particular number of transistors, the IC shrinks by half every 18 months • Enables incredibly powerful computation in incredibly tiny devices – Today’s ICs hold billions of transistors • The first Pentium processor (early 1990s) had only 3 million An Intel Pentium processor IC having millions of transistors
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2 Ve270 Introduction to Logic Design 5 The CMOS Transistor CMOS transistor – Basic switch in modern ICs gate source drain oxide A positive voltage here. . . .attracts electrons here, turning the channel between source and drain into aconductor. (a) IC package IC does not conduct 0 conducts 1 gate nMOS does not conduct 1 gate pMOS conducts 0 Silicon -- not quite a conductor or insulator: Semiconductor a Ve270 Introduction to Logic Design 6 Boolean Logic Gates - Building Blocks for Digital Circuits “Logic gates” are better digital circuit building blocks than switches (transistors) Ve270 Introduction to Logic Design 7 AND Gate Definition of AND operation Z = X Y means Z = 1 if and only if both X = 1 and Y = 1; Gate representation of AND operation and Truth Table 1 1 1 0 0 1 0 1 0 0 0 0 Z = XY Y X Truth Table 2-input AND gate Ve270 Introduction to Logic Design 8 Truth Table Truth table creates the relationship between the inputs and outputs – Must include all the inputs to the device in the left columns – Must include all the outputs of the device in the right columns
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This note was uploaded on 10/14/2011 for the course EE 270/370 taught by Professor Gangzheng during the Fall '11 term at Shanghai Jiao Tong University.

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L2+Basic+Logic+Gates - Switches Electronic switches are the...

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