Lecture 8. MOS Transistors; Cheap Computers; Everycircuit

Transcription

1 Lecture 8 MOS Transistors; Cheap Computers; Everycircuit Copyright 2017 by Mark Horowitz 1

2 Reading The rest of Chapter 4 in the reader For more details look at A&L 5.1 Digital Signals (goes in much more detail than we need) A&L MOS Devices M. Horowitz, J. Plummer E40M Lecture 7 2

3 Key Ideas From The Last Lecture State M+ M- Forward 4.5V 0V Reverse 0V 4.5V Off 0V (4.5V) 0v (4.5v) State M+ M- Forward true false Reverse false true Off false true false true 6 3

4 Key Ideas From The Last Lecture SwitchOn is either true or false; Limit is either true of false; Can represent Motor using two Boolean variables Forward is either true or false; Reverse is either true or false What is the Boolean expression for this FSM (Finite State Machine) Forward Reverse 4

5 By the End of Lecture, You Should Be Able To: Figure out whether a particular nmos or pmos transistor is on And connects its source and drain terminals together Use nmos and pmos transistors to build an inverter nmos devices connect output to Gnd pmos devices connect the output to Vdd Use EveryCircuit to simulate your circuits 5

6 MOS TRANSISTORS M. Horowitz, J. Plummer E40M Lecture 7 6

7 MOSFET a.k.a. MOS Transistor Are very interesting devices Come in two flavors pmos and nmos Symbols and equivalent circuits shown below Gate terminal takes no current (at least no DC current) The gate voltage * controls whether the switch is ON or OFF * actually, the gate to source voltage, V GS gate R on gate pmos nmos M. Horowitz, J. Plummer 7

8 nmos i-v Characteristics i i DS G D v Remember the resistor? S nmos is still a device Defined by its relationship between current and voltage But it has 3 terminals! Current only flows between the source and drain No current flows into the gate terminal! V DS M. Horowitz, J. Plummer 8

9 nmos MOSFET Characteristics G D S i Resistor? i gate v V GD or V GS 9

10 Simple Model of an nmos Device We will model an nmos device by components we know Resistor Switch NMOS Source = Gnd Gate = Gnd => Off Gate = Vdd => On i DS On This really simple model is suitable for applications where there s one value of On voltage. Off V DS M. Horowitz, J. Plummer 10

11 How Does an nmos Transistor Actually Work? (FYI not essential for this course) 11

12 Problem With nmos Device While an nmos device makes a great switch to Gnd It doesn t work that well if we want to connect to Vdd To turn transistor on Gate needs to be higher than source But we want the source to be at Vdd Oops 12

13 pmos i DS vs. V DS Characteristics V DS S G D Similar to nmos, but upside down! i DS Turns on when the gate-to-source voltage is < -1 V And the drain-to-source voltage should be negative Source should be the terminal with the higher voltage! M. Horowitz, J. Plummer 13

14 Simple Model of a pmos Device We will model an pmos device by components we know Resistor Switch NMOS Source = Vdd Gate = Gnd => On Gate = Vdd => Off V DS Off On i DS M. Horowitz, J. Plummer 14

15 How Does a pmos Transistor Actually Work? (FYI not part of this course) 15

16 nmos and pmos Devices Complement Each Other - CMOS PMOS Source = Vdd (+ supply) Gate = Gnd => On Gate = Vdd => Off NMOS Source = Gnd Gate = Gnd => Off Gate = Vdd => On 16

17 MOS Transistor Summary MOS transistors are extremely useful devices Almost all of your electronics uses them on the inside Including your phone, laptop, WiFi and Bluetooth, and your Arduino Come in two flavors nmos It is a switch which connects source to drain If the gate-to-source voltage is greater than V th (around 1 V) Positive gate-to-source voltages turn the device on. pmos It is a switch which connects source to drain If the gate-to-source voltage is less than V th (around -1 V) Negative gate-to-source voltages turn the device on and there s zero current into the gate! M. Horowitz, J. Plummer 17

18 MOS LOGIC GATES 18

19 What Does This Circuit Do? Is the output a logic function of the input? Consider V in = GND V DD pmos In Out nmos M. Horowitz, J. Plummer 19

20 Building Logic Gates from MOS Transistors Remember Boolean Logic? AND, OR, NAND = AND followed by Inverter Output is only low when A and B are true NOR = OR followed by Inverter Output is low when either A or B is true You can make them from MOS devices But only the inverting gates (NOR and NAND) 20

21 Building a CMOS NAND Gate Output should be low if both input are high (true) Output should be high if either input is low (false) 21

22 If You Look At Your Computer Chip It is just billions of transistors Creating many logic gates, and memory Take EE108A if you want know how we do that M. Horowitz, J. Plummer 22

23 HOW THE MOS TRANSISTOR CHANGED THE WORLD 23

24 First Computing Machines Were Mechanical Picture of a version of the Babbage difference engine built by the Museum of Science UK The calculating section of Difference Engine No. 2, has 4,000 moving parts (excluding the printing mechanism) and weighs 2.6 tons. It is seven feet high, eleven feet long and eighteen inches in depth 24

25 Moving Electrons was Easier than Moving Metal Building electronics: Started with tubes, then miniature tubes Transistors, then miniature transistors Components were getting cheaper, more reliable but: There is a minimum cost of a component (storage, handling ) Total system cost was proportional to complexity Integrated circuits changed that Printed a circuit, like you print a picture, Create components in parallel Cost no longer depended on # of devices 25

26 A Little History 1 st (Bipolar Junction) Transistor Christmas Eve 1947 By Bardeen, Brattain, and Shockley, Nobel Laureates in Physics st Integrated Circuit Jack Kilby, Nobel Laureate in Physics 2000 And Robert Noyce 1958 ( ml) (Courtesy of TI and Huff, SEMATECH) 26

27 What is an Integrated Circuit? A device having multiple electrical components and their interconnects manufactured on a single substrate. First IC 1958 Jack Kilby at TI Germanium A hack Wax support Made history Planar Process 1961 Bob Noyce at Fairchild Silicon Image from State of the Art Stan Augarten 27

28 Miniaturization Progress Over 50 Years From This To This To This Point Contact Transistor First Integrated Circuit Modern Microprocessor Modern silicon chips have 10 9 components in 1 cm 2 area. 28

29 Moore s Law Moore Intel Microprocessors The complexity for minimum component costs has increased at a rate of roughly a factor of 2 per year. Gordon Moore,

30 What This Means chip area shrinks to 17 mm die size shrinks to 0.05 mm 2 Chip edge is only twice the diameter of a human hair! 1985 (Intel 80386) 275,000 transistors 104 mm 2 ; 2640 Tr/mm (Intel 80486) 1,180,235 transistors 16,170 Tr/mm 2 Intel 10 nm CMOS * circa ,000,000 Tr/mm 2 or the original chip area could contain > 10 billion transistors! * Kaizad Mistry, Intel Technology and Manufacturing Day, March 28, 2017 M. Horowitz, J. Plummer 30

31 Take The Cover Off A Microprocessor Packaged die Cross section Single transistor Full wafer (100s of dies) modern wafers: mm diameter (8 12 inches) 31

32 Average Transistor Cost ($) No Exponential is Forever...but We Can Delay 'Forever, Moore ISSCC

33 EVERY CIRCUIT 33

34 Circuit Debugging For future labs you will be building more complex circuits You will build these circuits using your breadboards These circuits will contain many different components Including transistors Sometimes these circuits won t work the way you expect Perhaps your circuit is wrong Or perhaps you just connected it up wrong How do you debug it in either case? 34

35 Circuit Simulator We create a program to estimate how our circuit will behave The program shows the wiring in a nice way And makes it easy to probe the voltage and current It has built in voltage and current meters It also makes it easy to change component values So you can tune/play with your circuit You are going to use an easy to use simulator: Every Circuit 35

36 Every Circuit 36

37 Every Circuit Simple simulator that we will use for circuits 37

38 Quick Use Notes To connect two nodes, select one node, then select another node. To delete a single wire in a node, select the node, then select the wire, then press Delete. To maximize schematic area in browser window (remove circuit explorer on the left and circuit details on the right) click the rightmost icon in the menu below the schematic. 38

39 Every Circuit s Keyboard Shortcuts R : Rotate selected device F : Flip selected device A : Adjust parameter of a selected device T : Toggle selected switch W : Add / remove voltage of selected node or current of selected device to / from oscilloscope S : Adjust simulation speed Esc : deselect all Arrows : move selected component or workspace Plus / Minus : zoom in / out Space : start or pause simulation Delete : delete selected device or cut selected wire Ctrl + Z : Undo Ctrl + Y : Redo 39

40 Activate Your License 40

41 By the End of Lecture, You Should Be Able To: Figure out whether a particular nmos or pmos transistor is on And connects its source and drain terminals together Use nmos and pmos transistors to build an inverter nmos devices connect output to Gnd pmos devices connect the output to Vdd Use EveryCircuit to simulate your circuits 41