Transistors: Building blocks of electronic computing Lin Zhong ELEC101, Spring 2011

Key concepts Recap of PHY102 Ubiquity of resistance and capacitance Energy and power consumption Inverter: the simplest computing Transistor – Charge state 2

Electrons, charge, current Electron – Subatomic particle – ~9.109x gram Carbon atom ~2X grams – Elementary charge e - Charge – Q – Negative vs. positive – Coulomb: 6.25x10 18 e – Coulombs law Current – Flow of charge (electrons and electron holes) – I=dQ/dt 3

Field, potential and voltage Electric field – Force exerted on electric charge Electric potential Voltage: difference in potential – Ground (Gnd): 0 Volt – Supply voltage: Volt for modern integrated circuits Current flows from high potential to low – How about electrons? 4

Resistance and Ohms Law Opposition to the passage of a steady current – Conductor (e.g. metal) has negligible resistance – Insulator (e.g. plastic) has negligible passage – Semiconductor (silicon) Ohms Law – I=V/R or R=V/I R=ρL/A 5

Resistance is everywhere 6

Resistor Axial lead resistors 7

Voltage divider 8 Vdd Gnd R2 R1 V=Vdd*R2/(R1+R2)

Capacitor Charge holder Capacitance (capability to hold charge) – Charge per volt V C=Q/V

Capacitance is everywhere 10

Energy and power consumption 11 V Gnd R P=E/T =V*I =V 2 /R E=V*Q =V*I*T=V*(V/R)*T =V 2 *T/R

Energy and power consumption 12 V Gnd C Q=C*V + - Gnd C E=0.5*Q*V =0.5*C*V 2

13 Are resistors and capacitors enough? R=V/I C=Q/V Computing is about state Change Communication Storage

Think about a simple computer 14 Binary states for input and output: HIGH or LOW (1 or 0) How many different computers are there? 1)In=0 Out=0; In=1 Out=0 2)In=0 Out=1; In=1 Out=0 3)In=0 Out=0; In=1 Out=1 4)In=0 Out=1; In=1 Out=1 Can resistors and capacitors build them? How can we build 2)? In Out

How can we build an inverter? 15 In Out

16 Switch

Switch-based inverter 17 In Out Vdd Gnd

Lab: LED 18

What can one do with breadboard? 19 Breadboard prototype of the first IBM PC motherboard (1981)

Metal-Oxide-Semiconductor FET (MOSFET) Polysilicon Aluminum

MOSFET state 21

Controllable resistor 22 Gate control NMOS: resistance increases as gate voltage decreases Gate control PMOS: resistance increases as gate voltage increase Drain Source Drain

Controllable switch Change a state Communicate a state Store a state 23 Gate NMOS:ON with HIGH gate PMOS:ON with LOW gate

Change a state 24 Vdd Gnd Input Output Resistor LOW HIGH ?

Change a state (Contd.) 25 Vdd Gnd Input Output LOW HIGH Vdd Gnd Input Output Resistor LOW HIGH ? Resistor

Lab: NMOS and PMOS inverters 26

Whats wrong? 27 Vdd Gnd Input Output LOW HIGH Vdd Gnd Input Output Resistor LOW HIGH Resistor

Complementary MOS (CMOS) 28

Lab: CMOS inverter 29

Power consumption of Inverter Dynamic power – Remember capacitance is everywhere Static power 30

Delay of Inverter Capacitance and resistance are everywhere 31

A memory cell 32 Read/write Gnd Select