Gates and Circuits: Understanding Integrated Circuits

1. Chapter 4 Gates and Circuits

2. Integrated Circuits aka CHIPS • What’s in this thing????

3. Chapter Goals • How to make a gate from transistors • How to make integrated circuits using gates • The basic gates and their behavior • How gates are combined into (useful) circuits

4. Chapter Goals • Describe gates and circuits using: • Boolean expressions • Truth Tables • Logic Diagrams • Understand half adders, full adders, and binary addition circuits

5. Computers and Electricity • Transistor A device that can be used to make gates • Gate A device that performs a basic operation on bit(s) • Circuits Gates combined to perform more complicated tasks

6. Computers and Electricity • 3 ways to describe the same thing • Boolean expressions • logic diagrams • truth tables

7. Computers and Electricity • Boolean expressions A mathematical notation for expressing TRUE/FALSE logic • Example: F = AB + C

8. Computers and Electricity • Logic diagram A graphical representation of a circuit Each type of gate is represented by a specific graphical symbol • Truth table A table showing all possible input value and the associated output values

9. Gates • Let’s examine the processing of the following six types of gates • NOT • AND • OR • XOR • NAND • NOR

10. NOT Gate • A NOT gate accepts one input value and produces one output value • Aka “an inverter” Figure 4.1 Various representations of a NOT gate

11. AND Gate • An AND gate accepts two input signals • If the two input values for an AND gate are both 1, the output is 1; otherwise, the output is 0 Figure 4.2 Various representations of an AND gate

12. OR Gate • If the two input values are both 0, the output value is 0; otherwise, the output is 1 Figure 4.3 Various representations of a OR gate

13. NAND and NOR Gates • The NAND and NOR gates are essentially the opposite of the AND and OR gates, respectively Figure 4.5 Various representations of a NAND gate Figure 4.6 Various representations of a NOR gate 4–15

14. Constructing Gates • Transistor A device that acts as a switch, either open or closed (on or off) • A transistor has no moving parts, yet acts like a switch • It is made of a semiconductor material, which is neither a particularly good conductor of electricity, such as copper, nor a particularly good insulator, such as rubber

15. Constructing Gates • Transistor terminals • Source • Base • Emitter • If the electrical signal is grounded, it is allowed to flow through an alternative route to the ground (literally) where it can do no harm Figure 4.8 The connections of a transistor

16. Constructing Gates • It turns out that, because the way a transistor works, the easiest gates to create are the NOT, NAND, and NOR gates Figure 4.9 Constructing gates using transistors

17. Combinational Circuits • Consider the following Boolean expression A(B + C) Page 100 Page 101

18. Adders • At the digital logic level, addition is performed in binary • Addition operations are carried out by special circuits called, appropriately, adders

19. A Half Adder • Recall that 1 PLUS 1 = 10 in base two • In other words: 0 with a carry of 1

20. Half Adder Circuit • Two Boolean expressions: sum = A  B carry = AB Page 103

21. A Full Adder • A circuit called a full adder takes the carry-in value into account

22. Integrated Circuits • We can combine 4 full adders to make a Four-bit Adder Circuit (about 60 transistors)

23. Integrated Circuits aka CHIPS • What’s in this thing???? Chip Fabrication Technology

24. Integrated Circuits • Integrated circuit (also called a chip) A piece of silicon on which many gates have been embedded

25. “Silicon Valley” • Sand is mostly Silicon Dioxide

26. “Silicon Valley” • Silicon Dioxide ingots and wafers

27. “Silicon Valley” • Photolithography “Printed” with lots of copies of some circuit

28. Integrated Circuits aka CHIPS • What’s in this thing???? Computer Architecture: Combining Abstractions into larger Abstractions

29. Transistors and Gates

30. Integrated Circuits An simple chip containing 4 independent NAND gates (about 8 transistors)

31. Integrated Circuits • A four-bit Full Adder Circuit

32. Integrated Circuits • An Arithmetic Logic Unit (ALU) has adders and other things in it

33. Integrated Circuits • A simple Central Processing Unit, or CPU has an ALU and other things • Take Engineering 303 Digital Logic Design!!

34. CPU Chips • A recent CPU chip (Intel Nehelem) 731 Million transistors

35. The Future of the IC • Global Competition • Further Integration (ARM)