exam for Electronic Engineering

4/2/2018

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EE 1301: MODERN ELECTRONIC TECHNOLOGY

SESSION #27: SOUND WAVES AND ELECTRONIC TECHNOLOGY

04/02/2018 Instructor: Joseph Cleveland, Ph.D.

Email: [email protected]

Thought for the Day

Aim at heaven and you will get earth thrown in. Aim at earth and you get neither.

C. S. Lewis

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Topics

• Sound and Electronic Technology – Microphones

– Amplifiers

• Preview of Lab #8: The Amplifier

• Wednesday, 4/4, review

• Friday, 4/6, exam #2

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Review of Sound Concepts

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Standing Waves and Resonance

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http://hyperphysics.phy- astr.gsu.edu/hbase/waves/string.html

Harmonic resonances in strings

L

⁄

⁄

⁄

⁄

⁄

f1

2f1

3f1

4f1

5f1

6f1

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Complex Waves and Spectra

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6600 Hz 4400 Hz

A m

p li

tu d

e

A m

p li

tu d

e

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Microphones

How they work

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Condenser (Capacitor) Microphones

The changing pressure of the sound wave causes the diaphragm to move back and forth.

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Capacitor

Condenser Microphones

• Recall the structure of the capacitor (condenser)

~

• If d decreases, C increases

• If d increases, C decreases

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Condenser Microphones …

• Attach a battery to the capacitor:

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48 V ++++ ++++

- - - - - - - - d1

R If d shrinks, C increases so stored charge Q increases: current flows into C.

I 

R

48 V

++++ ++++

- - - - - - - -

d1

 I If d expands, C decreases so stored charge Q decreases: current flows out of C.

Ribbon Microphones

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Magnet

Step-Up Transformer

Corrugated Ribbon

• The changing pressure of the sound wave causes the ribbon to move back and forth in the magnetic field

• This causes current to flow in and out of the transformer as a replica of the wave

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Amplifiers

• What is an “Amplifier”?

An electronic device for increasing the amplitude or power of electronic signals.

• Widely used in – Sound reproduction as in MP3 player

– Mobile phones in speech and music

– DVD players

– Cameras to amplify image voltage

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Amplifier Types

• Amplifier circuits had many different forms

• Bipolar junction transistors (NPN, PNP) – Common emitter

– Common base (Lab #8)

– Common collector

• MOSFETs (n-channel, p-channel) – Common source

– Common gate

– Common drain

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NPN Transistor Operation

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FWD

REV

Recall that the voltage on the base controls the base current

~0.7 V

The larger the base current, the larger the collector current

collector

emitter

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Common emitter circuit

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MP3 Signal

Emitter is common to input and output

Common Emitter Amplifier

• Apply a musical tone to the input

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A small input signal

produces a large output signal

Ic

MP3 Signal

Inverting Amplifier

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• If the input is too large or the supply voltage (VDD) is too low, clipping occurs

• A highly distorted signal

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Amplifier Circuit for Sound

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ic

MP3 Signal

MP3 Sound

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Structure of a Speaker

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As the current changes, the coil moves back and forth

Current

Current in coil produces a magnetic field

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Lab #8: A simple Transistor Amplifier

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Common Base Amplifier

• Base is common to input and output

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Rbias

RE

9V

Common Base Amplifier …

• When the voltage on the input increases, the emitter voltage increases and the base-emitter voltage decreases; the collector current decreases

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.

470 

470 

9V

Ic

increases

-2 V offset

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Common Base Amplifier …

• When the voltage on the input decreases, emitter voltage increases and the base-emitter voltage increases; the collector current increases

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.

470 

470 

9V

Ic

decreases

-2 V offset

Common Base Amplifier …



A Non-Inverting Amplifier

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. 2.2 4.7

470 

470 

9V

Ic

0V

0.5 V

5 V

-2 V offset

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End of Session