Semiconductor Devices and MicroelectronicsA subtopic of Basic Electronics

First Electronic Devices

• Contain several hundred vacuum tubes occupying one large room• Vacuum tubes consume

several thousand watts of electrical power

Semiconductors/Transistors

• Occupies a small side table• Uses only several

watts• Small-sized and more

efficient

Microelectronics

Microelectronics is the branch of electronics which deals with

small, miniaturized components

Diodes

•The simplest semiconductor device•has many applications, from simple indicators and AC/DC conversion to voltage regulation and appliance protection.

Kinds of Diodes

A diode is forward-biased when the voltage on the positive leg is higher than on the negative leg then current flows through the diode (the resistance Is very low)

Kinds of Diodes

A diode is reverse-biased when the voltage is lower on the positive leg than on the negative leg then the current does not flow (the resistance is very high).

Cathode and Anode

Types of Diodes

Junction Diode • the first type of

diode developed• Name derived from

the principle of the diode, the positive-negative or p-n “junction”

Types of DiodesZener Diode • Might be called as a voltage

reference diode.• used to provide a certain

voltage to a circuit, determined by the rating of the zener diode.• If the zener is forward-biased,

then the voltage will just be equal to the forward biased voltage of an ordinary diode.

Types of DiodesLight Emitting Diode • LED is a special kind of

diode.• When current flows

through from the anode to the cathode, it lights up• The higher the current

passing through the LED, the brighter the light

Types of Diodes

Photodiode s• The current flow depends on

whether the diode is exposed to light within a given range of wavelength• Absence of light turns the diode in

reverse-biased mode• usually paired with a light source,

which could be as simple as ordinary or ambient light, to as restrictive as an infrared LED, to as state-of-the-art as lasers.

Other Diodes

• Optoisolators• Tunnel diodes• Power diodes• Varactor or tuning diodes• Schottky Barrier diodes

Rectification

• the process of making a signal flow in one direction only• the converting of a signal from an alternating current (AC) to direct current (DC).

Two ways of rectifying a signala) Half –wave Rectification• the process of converting

of a signal with both positive and negative phases to a DC signal with a single phase only, either positive or negative (not both). The other phase is clipped or removed.

Two ways of rectifying a signalb) Full –wave Rectification• also converts an AC signal to a

single phase but this time instead of clipping the other phase, it cpnverts it to the opposite phase.

• Two ways of creating a full-wave rectifiera) By using two diodes, with a

center top as ground reference,b) via a diode bridge

The TransistorTransistors are basic components in all of today’s

electronics. They are simple switches that can turn things on and off.

It is another semiconductor with a wide range of applications, from simple switching states to amplifying signals.

Three types of transistors:a) Bipolar Junction Transistors (BJTs)

b) Unipolar Junction Transistors (UJTs)

c) Field Effect Transistors (FETs)

Bipolar Junction TransistorsThe BJT is a three-terminal device.

Parts of a Transistor:a) Base

b) Collectorc) Emitter

Two basic transistor configurationsa) n-p-n transistor

- a p-type semiconductor is sandwiched between two n-type semiconductors.

b) p-n-p transistor- a n-type semiconductor is sandwiched between two p-type semiconductors.

Basic CircuitThe Base (B) is the On/Off switch for the

transistor. If a current is flowing through the Base, there will be a path from the Collector (C) to the Emitter (E) where current can flow (The Switch is On). If there is no current flowing to the Base, then no current can reach the Emitter from the Collector (The Switch is Off)

Basic Circuit

Basic CircuitWe will use Ohm’s Law to find the current in the path

from the Input to the Base of the transistor and the current flowing through the LED. To do this we need to use two basic facts about the transistor.1. If the transistor is on, then the Base voltage is 0.6 volts higher than the Emitter voltage VBE = 0.6V2. If the transistor is on, the Collector voltage is 0.2 volts higher than the Emitter voltage VCE = 0.2V

Basic CircuitSo the base current ib (current flowing through the

2.2K resistor) similar to this circuit.

And is given by ib = VB/Rb = (9 – 0.6)/2200 = 0.0038 A = 3.8 mA

The current flowing through the 330-ohm resistor can be derived from this circuit,

Basic CircuitSo the base current ib (current flowing through the

2.2K resistor) similar to this circuit.

And is given by ib = VC/RC = (9 – 0.6)/2200 = 0.0038 A = 26.7 mA

The current flowing through the 330-ohm resistor can be derived from this circuit,

Basic CircuitMathematically,

ic = Vc/RC = (9 – 0.2)/330 = 0.0224 A = 26.7 mAIf we want more current flowing through the

collector, we can use a smaller resistor (instead of 330). This means we can control things that use a lot of power with cheap, low power circuits. The is called current driving