Basic electronics stuff

Date created: 24-Mar-2021

Some notes on basic electronics stuff. Derived mostly from Wikipedia articles.

Band gap

Gap between top of valence band and bottom of conducting band.
An energy gap.
Usually represented in electron volts (eV).
Energy required to promote a valence electron (electron from valence band) to make it a conducting electron (electron in conducting band).
Band gap: ([image](https://commons.wikimedia.org/wiki/File:Band_filling_diagram.svg))
- large: insulator
- smaller: semiconductor
- tiny or none: conductor

Valence electron

Electrons in the outer shell of the atom (valence shell).
Determines the element's chemical properties.
Participates in bond formation to form covalent bonds.
Atom with a closed shell means chemically inert (as in inert gases like He, Ne, Ar, etc).

Conduction electron

Free to move in the crystal lattice and serve as charge carrier for electric current.

Electron holes

Lack of electron at a point where an electron could exist.
Like a positive charge due to the absence of the electron's negative charge => a net positive charge.
Holes in metals and semiconductor crystal lattices can flow the way electrons can.
Plays important role in the operation of diodes, transistors, etc.
If an electron is excited to a higher state, a hole is created at its former position.

Diode

Conducts power only in one direction.
Has two terminals.
High resistance (theoretically infinite) in one direction
Low resistance (theoretically zero) in another direction.
Can be combined with other components to create logic gates like OR and AND => Diode Resistor Logic (DRL)

Extrinsic semiconductor

Semiconductor that has been doped.

Intrinsic semiconductor

Undoped semiconductor.
Pure semiconductor without significant amount of dopants.
Number of excited electrons = Number of electron holes. ie, n=p.

Charge carrier

Majority charge carrier: The more abundant charge carrier
Minority charge carrier: The less abundant charge carrier

Fermi level (of a solid state body)

Amount of thermodynamic work that needs to be done to add an extra electron to that solid-state body.

Depletion region

An insulating region within a conductive, doped semiconductor.
The mobile charge carriers of this region have been diffused away (for holes?) or forced away (for electrons?) by an electric field.
The only remaining elements here are the ionized donor (result of extra electron addition) or acceptor impurities (result of hole creation).
The region is formed out of a conducting region by removing all free charge carriers => No carrier left to carry current => it becomes an insulating region.
Diodes, BJTs, FETs, etc rely on this phenomenon.

p-type semiconductor

Made by doping an intrinsic semiconductor with an electron acceptor element -> holes created.
Positive charge due to holes.
Majority carrier: Holes
Minority carrier: Electrons
Dopant for Silicon could be Boron or Gallium

n-type semiconductor

Made by doping an intrinsic semiconductor with an electron donor element -> extra electrons.
Negative charge due to extra electrons.
Majority carrier: Electrons
Minority carrier: Holes
Dopant for Silicon could be Phosphorus or Arsenic.

p-n junction

Created by doping.
Boundary between two types of semiconductor materials:
- p-type
- n-type
Electric current passes in only one direction because
- p side: has excess holes
- n side: has excess electrons
A diode can be made from a single p-n junction
A BJT consists of two p-n junctions (either as p-n-p or as n-p-n)

Transistor

Obtain a controlled flow of electrons.

Can amplify or switch electronic signals.
Usually has three terminals.
Voltage applied to one pair of terminals control current through another pair of terminals?
Controlled power is the output
Controlling power is the input
Controlled power could be greater than the controlling power => amplification

—

Bipolar Junction Transistor (BJT):

         Emitter
    /
Base---|
    \
         Collector

Base regulates the flow from emitter to collector.

—

Field Effect Transistor (FET):

         Source
    /
Gate---|
    \
         Drain

PLA

Programmable Logic array.
Can implement combinational logic.
There is an AND-plane and an OR-plane, gates of both are programmable.
n input and m output means:
- 2ⁿ AND gates in AND-plane
- 2ᵐ OR gates in OR-plane
Different from Programmable Array Logic (PAL)
- PAL has programmable AND, but OR is fixed.
Could be used to 'implement control over a datapath'. ²⁰

Digital logic families

Diode Resistor Logic (DRL)

Construction of Boolean logic gates with diodes.
Popular in early computers.
Not all logic gates can be constructed only with diodes. Only AND and OR.
Advantage: Simple.
Disadvantage: Lack of an amplifying stage in each gate (so DRL normally limited to single stage?)

Resistor Transistor Logic (RTL)

Input network = resistors
Switching done by BJTs
Earliest class of 'transistorized' digital logic circuit.
First digital logic family to be produced as an IC.

Diode Transistor Logic (DTL)

Uses diodes and invertor logic (ie, NOT).
Direct ancestor of TTL.
Came after RTL.
Logic gates with diodes and amplification via transistors

Transistor Transistor Logic (TTL)

Built from BJTs.
Transistors are used to do both the logic function and the amplifying function.
TTL ICs were used to build computer processors before the advent of VLSIs.

Field Effect Transistor (FET)

A unipolar transistor: either electron or hole is used as charge carrier. Not both.
Uses an electric field to control flow of current (hence the term FET?)
Has three terminals:
- Source
- Gate
- Drain
Voltage is applied to gate and the conductivity between source and drain is influenced.
MOSFET: Most widely used FET.

Bipolar Junction Transistor (BJT)

Uses both electrons and holes as charge carriers (hence the term bipolar?)

Impedance (in electronics)

High impedance

Allows lesser amount of current to flow through in relation to the applied voltage.
High impedance circuits are low current and (potentially?) high voltage.
Tristate in digital circuits => neither high state nor low state. Effectively an open circuit.
- Basis of bus systems in computers.

Low impedance

Low impedance circuits are high current and low voltage.

7-segment display

Basically a bunch of LEDs bundled together.

      a
   -------
  |       |
f |       | b
  |   g   |
   -------
  |       |
e |       | c
  |       |      
   -------     ---
      d         p

Possible configurations:

Common cathode
Common anode

Got to use a multimeter to see which type of 7-segment display it is.

| n | a | b | c | d | e | f | g | p |
|---+---+---+---+---+---+---+---+---|
| 0 | 1 | 1 | 1 | 1 | 1 | 1 |   |   |
| 1 |   | 1 | 1 |   |   |   |   |   |
| 2 | 1 | 1 |   | 1 | 1 |   | 1 |   |
| 3 | 1 | 1 | 1 | 1 |   |   | 1 |   |
| 4 |   | 1 | 1 |   |   | 1 | 1 |   |
| 5 | 1 |   | 1 | 1 |   | 1 | 1 |   |
| 6 | 1 |   | 1 | 1 | 1 | 1 | 1 |   |
| 7 | 1 | 1 | 1 |   |   |   |   |   |
| 8 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |   |
| 9 | 1 | 1 | 1 | 1 |   | 1 | 1 |   |

There is also:

9-segment display
14-segment display
16-segment display

Arduino Uno

Arduino uno uses an ATmega microcontroller.

(Hadn't known that microcontrollers are sometimes referred to as 'MCU's, which stands for Micro-Controller Unit.)

        +--------+         
        |        |                
        |        |-- D19          
        |        |-- D18          
        |        |-- AREF
        |        |-- GND
        |        |-- D13          
IOREF --|        |-- D12          
RESET --|        |-- D11          
+3.3V --|        |-- D10          
  +5V --|        |-- D9           
  GND --|        |-- D8           
  GND --|        |                
  Vin --|        |-- D7           
        |        |-- D6           
   A0 --|        |-- D5           
   A1 --|        |-- D4           
   A2 --|        |-- D3           
   A3 --|        |-- D2           
   A4 --|        |-- D1           
   A5 --|        |-- D0           
        +--------+

A0-A5 are analog pins. (ADC, Analog to Digital, at 10 bit precision actually. So ranges in [0,1024) integer interval.)

Doubts:

purpose of two different voltage levels? 3.3v and 5v.
Vin is for external power supply?

Links:

PCB

Printed Circuit Board

Terms:

trace
via

Layers of a PCB

Outermost to innermostʳ:

Substrate
- An insulator.
- Can separate two conducting layers in case of multi-layer PCBs
- Could be made of fibre glass. Or of paper (eg: FR1ʳ)
Copper layer
- The conducting part.
Soldermask
- Made of resin?
- Responsible for the usual green colour of PCBs.
Silkscreen
- Contains labels for easy identification.

THT vs SMT

Ways of placing components onto the taped out PCB.

Through-Hole Technology
- Considered obsoleteʳ
- Holes are drilled in PCB and component is soldered after inserting the pins through these holes.
Surface-Mounted Technology
- Surface mounted device (SMD)
- There are pads on to which pins of components are placed. No holes need be drilled onto the PCB.
- Better than THT in most aspects. Cheaper, more accurate.

Fiducial marker

For helping 'pick-and-place assembly machines'
- ie, assembly of components onto the PCB being done by a machine.
Especially common for square or rectangular designs
Global fiducials: Usually place in diagonally opposite corners
Local fiducials: Place at a particular point ʳ

Links:

Other electronic stuff of interest

Fourier transform: Convert signal from one domain to another
- Example: time domain to frequency domain (or vice versa)
- https://www.mathsisfun.com/calculus/fourier-series.html
pmos
nmos
Forward bias, reverse bias operation of p-n junction
Breakdown voltage of a p-n junction
Reverse voltage
inversion layer
cmos
npn
pnp
p channel
saturation in transistors
Emitter Coupled Logic (ECL)
MOS
MOSFET