ECE492 Section 1 Notes

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Welcome! Notes for Spring 2022 Electronic Circuits course. Will make this more pretty as things evolve.

My goal is to make Electronic Circuits so easily digestible, you could teach a middle schooler. We'll see if this works.

Prologue

Hey how are you. I will insert something here later. :)

Section 1.1

We first need to consider the following materials:

  • Conductors
  • Insulators
  • Semiconductors

Consider the concept of the charge for Oxygen (O):

  • 8 protons around the nucleus
  • 8 electrons (two on the inner orbit, 6 on the outer orbit).

Let's look at the outer most orbit in context with a conductor:

  • There are two bands: valency and conduction.
  • Electrons are always in the valency band.
  • In between, there is an energy gap, which is approximately 0 (meaning electrons can move freely between valency band and conduction band).
  • That is the reason why conductive materials act as they do.

Let's look at the outer most orbit in the context of insulators:

  • There are two bands: valency and conduction.
  • Electrons are always in the valency band.
  • In between, there is an energy gap, which is very high (meaning electrons have a very hard time moving between the valency band and conduction band).
  • That is the reason insulators, are well, insulators (or their property is insulative).

Let's look at the outer most orbit in the context of semi-conductors:

  • There are two bands: valency and conduction.
  • Electrons are always in the valency band.
  • In between, there is an energy gap, which is exactly 1.12eV (1eV = 1.602 * 10-19J).
  • Once electrons are in the conduction band, the semi-conductor will act as a conductor.

This entire class is based on semi-conductor materials.

What is a semiconductor?

It sometimes allow current, and sometimes it doesn't.

Semi-conductors only have 4 electrons in its outermost orbit.

  • Carbon
  • Silicon
  • Germanium
  • Lead

What's the best two?

  • Silicon and Germanium

Consideration of Silicon:

  • Silicon will acquire other silicon atoms to form a covalent bond.

Now let's take a Silicon atom:

  • Take a pure silicon atoms and put energy to them: go from insulator to conductive properties, and electrons from the furthest orbit detach and jump to another position.
  • When electrons detach, it leaves a hole where it once was, that is viewed as a positive charge for clarity.

Doping: Adding impurity to a pure semiconductor material.

  • Tri-Valent Impurity: majority of "holes" (positive charge), also know as P-type semiconductor.
  • Penta-Valent Impurity: majority of electrons, also known as N-type semiconductor.

Let's take Aluminum for Tri-Valent example:

  • Pair the Aluminum with Silicon atoms, knowing that Aluminum has an outer electron count of 3.
  • Silicon will be bounded to the three outer Aluminum electrons, but 1 Silicon will be left.

Let's try Phosphorous for Penta-Valent example:

  • Pair Phosphorous with Silicon atoms, knowing that Phosphorous has an outer electron count of 5.

Now what is P-N Junction? It's a diode.

  • A P-type semiconductor connected to an N-type semiconductor.
  • Recall that P-type just has a lot of "holes" (positive).
  • Recall that N-type has a lot of electrons (negative).
  • Shouldn't these holes and electrons combine? Electric field is present due to electrons on the N-type side of the P-N junction. This electric field does not allow for combining.
  • There is an anode and a cathode on the P-type and N-type side respectively. A diode can be represented with A -> C.
  • Now let's connect a battery on each side of the junction, and we supplement 0.5V.
  • The electric field barrier becomes thinner and thinner, but not completely gone.
  • Now apply 1.0V, the electrons and holes will push against the junction.

Now consider a reverse biased diode:

  • A diode where the energy source charge is reverse from the P-N junction.
  • Holes to negative and electrons to positive.

Important consideration: A P-N Junction (diode, or biased/reversed biased diode) allows current in only one direction.

What are the V-I characteristics of the P-N Junction/Diode:

  • What is PIV? Peak Inverse Voltage.
  • Consider the graph below for a typical V-I characteristic of a diode.

VIcharacteristics.jpg

Therefore, important considerations added for P-N Junction diode:

  • A P-N Junction (diode, or biased/reversed biased diode) allows current in only one direction.
  • Acts like a closed switch in forward biased condition.
  • Acts like an open switch in reversed biased condition.

Now consider the following example: Find the current passing through each diode.

  • We'll need to break the problem apart.
  • Current always flows from higher potential to lower potential.
  • Assume ideal diode.

Let's break the problem down:

  • Step 1: Fill me in. :)

Assignment 1.1

We'll take this and plug it into to find x2: