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Transistors: The Fundamental Units of Computing Systems

Explore the essential role of transistors, resistors, and capacitors in electronic computing. Understand their properties, applications, and significance in building electronic devices. Learn about Ohm's Law, circuits, and power consumption in computing. Dive into the basics of semiconductors, FETs, and MOSFETs for a comprehensive insight into modern computing. Discover how transistors enable state changes, communication, and storage in electronic systems.

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Transistors: The Fundamental Units of Computing Systems

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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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