20.4 Electronic Devices

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20.4 Electronic Devices

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We are going to learn…

How electronic signals convey informationHow vacuum tubes control electron flowHow are semiconductors usedThe benefits of using microchips

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Electronic or ElectricalThe science of using electric current to process or

transmit information is electronics.If it uses electricity, but does not process or transmit

information, it is an electrical device (not an electronic device).

Information is the key.Toasters and lamps are

electrical.Cell phones and computers

are electronic.

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Electronic SignalsThe information of an electronic device is carried by an

electronic signal.An electronic signal is information sent as patterns in

the controlled flow of electrons through a circuit.



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Electronic SignalsSo we create a signal by either altering the voltage or

turning the current on and off.Other electronic devices can interpret these patterns of

voltage or current and make them into something meaningful.

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Electronic SignalsElectronic devices convey information with electrical

patterns called analog and digital signals.An analog signal is a smoothly varying signal produced

by continuously changing the voltage or current in a circuit.

Information is encoded in the strength or frequency of the analog signal.

Radio stations encode music with an analog signal.



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Electronic SignalsA digital signal encodes information as a string of 1’s

and 0’s.We do this by turning current on and off.The number 1 is communicated when the current is on.0 is when the current is off.Morse code was the first

example of a digital electronic signal.



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Electronic SignalsDigital signals are more reliable than analog signals.If you damage a digital signal, you will still read a 1 or a

0. However, if you damage an analog signal, you get a distorted “noise” in the signal.



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Vacuum TubesRemember, to create an electronic signal, you must be

able to control the flow of electrons.A vacuum tube was used to control electron flow in early

electronic devices.It was a very useful device.Vacuum tubes can change

alternating current into direct current, increase the strength of a signal, or turn a current on or off.



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Vacuum TubesOne useful type of vacuum tube is a cathode-ray tube

(CRT). Many televisions contain CRTs.One side of the CRT has three metal plates that emit

electron beams.



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Vacuum TubesThe electrons are emitted at one end of an airless tube

and strike a glass surface on the other end.The glass is coated with phosphors that glow red, green,

or blue in response to the electron beams.Vacuum tubes are usually too large for use in small

electronic devices.

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SemiconductorsA semiconductor is something that conducts current…

sometimes.The conditions have to be right in order for a

semiconductor to conduct current.Most semiconductors are made with silicon or

germanium (which are poor conductors until you add small amounts of other elements to them).



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SemiconductorsThere are two types of semiconductors: “n-type” and “p-

type.”In n-type semiconductors, the current is a flow of

electrons.In p-type semiconductors, it appears as though positive

charge flows.

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SemiconductorsP-type semiconductors have “holes” in them that are

positively charged.N-type semiconductors have weakly bound electrons

that can flow.By themselves, n-type and p-type semiconductors

cannot do much. But when joined together, electrons in the n-type are attracted toward the positively charged holes in the p-type.

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SemiconductorsAs electrons jump from hole to hole, it looks like a flow of

positive charge because the locations of the positive charges change.

These semiconductors are then used in diodes, transistors and integrated circuits.

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Solid-State ComponentsSemiconductor devices were first used in the late

1940s and were named “solid-state components” because they used solids rather than vacuum tubes to control current.

Most modern electronic devices are controlled by solid-state components.

Three of the most useful solid-state components are diodes, transistors, and integrated circuits.

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DiodesA diode is a solid-state component that combines an n-

type and p-type semiconductor.The goal of a diode is to allow current to flow in one

direction, but not the other.



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DiodesWhen a voltage is applied across a diode, the electrons

flow from the n-type to the p-type semiconductor.There is no current if voltage is applied in the opposite

direction.Because the current can be in

only one direction, a diode can change alternating current to direct current.

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TransistorsA transistor is a solid-state component with three layers

of semiconductors and at least three terminals for connection to an external circuit.

The goal of a transistor is to act like a switch or amplifier for current.



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TransistorsA voltage or current applied to one pair of the transistor's

terminals changes the current flowing through another pair of terminals.

It can also be used as an amplifier. A small voltage applied to one side of the transistor produces a large voltage on the other side.

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Integrated CircuitsAn integrated circuit (also called a microchip) is a thin

slice of silicon that contains many solid-state components.

The components are carefully built layer by layer on the silicon base.

They perform like a network of vacuum tubes, but they need only a fraction of the space.

Microchips are used in cell phones, computers, iPods.



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Integrated CircuitsA microchip the size of your fingertip can contain millions

of components!These microchips are also incredibly fast compared to

vacuum tubes since the charges don’t have to travel very far to get from point to point.

The smaller the chip, the faster the speed.

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Communication TechnologyA computer is a programmable device that can store

and process information.Today you find microchips in all sorts of devices that you

wouldn’t call computers, namely cell phones.A cell phone uses all three of the solid-state

components.



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Communication TechnologyTransistors amplify the phone’s incoming signal.Capacitors store electric charge and allow cell phones to

store data such as phone numbers.Diodes maintain proper voltage levels in the circuits.All of these things are wired

into an integrated circuit.

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20.4 Electronic Devices