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AMPLIFIERSAMPLIFIERS

2

• Demostrate Transistor Amplification

• Determine Transistor Biasing.

• Explain Transistor Regions - Emitter, Base, Collector.

• Explore Transistors as Switches

Objectives

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Amplifier Out

InGain=

In

Out

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N

P

NThe collector is lightly doped. C

The base is thin and is lightly doped.

B

The emitter is heavily doped. E

NPN Transistor Structure

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The C-B junction is reverse biased.

N

P

N

NPN Transistor Bias

C

B

E

No current flows.

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The B-E junction is forward biased.

N

P

N

NPN Transistor Bias

C

B

E

Current flows.

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When both junctionsare biased....

N

P

N

NPN Transistor Bias

C

B

E

Current flowseverywhere.

Most of the emitter carriersdiffuse through the thin base

region since they are attractedby the collector.

Note that IB is smallerthan IE or IC.

IC

IB

IE

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N

P

N C

B

E

Although IB is smallerit controls IE and IC.

IC

IB

IE

Note: when the switch opens, all

currents go to zero.

Gain is something smallcontrolling something large

(IB is small).

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Amplifier Out

InGain=

In

Out

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The C-B junction is reverse biased.

N

P

N

NPN Transistor Bias

C

B

E

No current flows.

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The B-E junction is forward biased.

N

P

N

NPN Transistor Bias

C

B

E

Current flows.

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When both junctionsare biased....

N

P

N

NPN Transistor Bias

C

B

E

Current flowseverywhere.

Most of the emitter carriersdiffuse through the thin base

region since they are attractedby the collector.

Note that IB is smallerthan IE or IC.

IC

IB

IE

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N

P

N C

B

E

Although IB is smallerit controls IE and IC.

IC

IB

IE

Note: when the switch opens, all

currents go to zero.

Gain is something smallcontrolling something large

(IB is small).

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Transistor Structure and Bias QuizThe heaviest doping is found in the ___________ region.

emitter

The thinnest of all three regions is called the ____________.

base

The collector-base junction is ___________ biased. reverse

The base-emitter junction is ____________ biased. forward

The majority of the emitter carriers flow to the ___________. collector

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