Jupyter at Bryn Mawr College
Public notebooks: /services/public/dblank / CS240 Computer Organization / 2015-Fall / Notes

1. Transistors

Table of Contents

1.1 Low-level Physics

  • Solid state - not mechanical, electrons do all of the work
  • switch - on/off

1.1.1 How semiconductors work

Review:

  • silicon "crystals" - matrix/lattice; insulator - doesn't conduct electricity
  • But "doping" turns silicon into a conductor
    • phosphorus - extra electron/proton; conductor N-type (negative charge carrier, electrons)
    • boron - one fewer electron/proton; conductor P-type (positive charge carrier, holes)
    • Not charged! But have ability to move electrons
  • interesting place: P-N, N-P boundaries
  • no charge carriers in "depletion region" - insulator
    • one direction, gets larger, other gets smaller
    • diode
  • semiconductor

1.1.2 Switches and Logic Gates

Breadboard:

LED:

  • Light-emitting Diode

1.2 Circuit

PNP 2N4403

  1. Look at number on part, 2N4403
  2. Look up "datasheet": http://pdf.datasheetcatalog.com/datasheet/philips/2N4403.pdf
  3. Get specifications:
    • Collector, Emitter, and Base
    • PNP

<img src="../images/pnp.png"/ width="500">

1.3 Simulation

Change the voltage on the base to allow conductivity on the wire:

http://www.falstad.com/circuit/e-pnp.html

MOS Transistors

https://en.wikipedia.org/wiki/MOSFET

  • p-type: when gate is supplied with voltage, it acts like an open switch (open circle)
  • n-type: when gate is supplied with voltage, it acts like a closed wire (no circle)

CMOS: complementary metal-oxide semiconductor, made up of n-type and p-type transistors

http://solarwiki.ucdavis.edu/The_Science_of_Solar/Solar_Basics/D._P-N_Junction_Diodes/I._P-Type,_N-Type_Semiconductors

Inverter

NOR

NAND Gate

Abstraction!

Decoder

2-input, 4-output decoder

Multiplexer (mux)

2-input, 1-output

Full-adder

Bit adder:

  • 3-input (bit 1, bit 2, carry bit)
  • Output: sum and carry

Repeat for each bit.

PLA - Programmable Logic Array

All combinations (AND array), pick which ones give true (OR array)

  • Can compute any logical function

Registers

R-S Latch

R = 1, S = 1 then latch holds its memory (whatever that is).

  • R = 1, momentarily set S = 0, latch is 1
  • S = 1, momentarily set R = 0, latch is 0

Gated D Latch

  • D is the data in
  • WE (write enable) says to store data in latches

Register

Series of Gated D Latches, one per bit.

Memory

Decoders and muxes.