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Transistors: Building blocks of electronic computing

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. Electrons, charge, current. Electron

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Transistors: Building blocks of electronic computing

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

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

  3. Electrons, charge, current • Electron • Subatomic particle • ~9.109x10-28 gram • Carbon atom ~2X10-23 grams • Elementary charge e- • Charge • Q • Negative vs. positive • Coulomb: 6.25x1018 e • Coulomb’s law • Current • Flow of charge (electrons and electron holes) • I=dQ/dt

  4. Field, potential and voltage • Electric field • Force exerted on electric charge • Electric potential • Voltage: difference in potential • Ground (Gnd): 0 Volt • Supply voltage: 1.2-5 Volt for modern integrated circuits • Current flows from high potential to low • How about electrons?

  5. Resistance and Ohm’s 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) • Ohm’s Law • I=V/R or R=V/I • R=ρ∙L/A

  6. Resistance is everywhere

  7. Resistor • Axial lead resistors

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

  9. Capacitor • Charge holder • Capacitance (capability to hold charge) • Charge per volt - + V C=Q/V

  10. Capacitance is everywhere

  11. Energy and power consumption V E=V*Q =V*I*T=V*(V/R)*T =V2*T/R R P=E/T =V*I =V2/R Gnd

  12. Energy and power consumption V Gnd + C Q=C*V C - E=0.5*Q*V =0.5*C*V2 Gnd Gnd

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

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

  15. How can we build an inverter? Out In

  16. Switch

  17. Switch-based inverter Vdd Out In Gnd

  18. Lab: LED

  19. What can one do with breadboard? Breadboard prototype of the first IBM PC motherboard (1981) http://www.yourdictionary.com/computer/breadboard

  20. Metal-Oxide-Semiconductor FET (MOSFET) Polysilicon Aluminum

  21. MOSFET state

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

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

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

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

  26. Lab: NMOS and PMOS inverters

  27. What’s wrong? Vdd Vdd Resistor Output Input Input Output HIGH HIGH LOW Resistor LOW Gnd Gnd

  28. Complementary MOS (CMOS)

  29. Lab: CMOS inverter

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

  31. Delay of Inverter • Capacitance and resistance are everywhere

  32. A memory cell Read/write Select Gnd

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