small signal amplifiers - lesson 1 - intro to amplifiers

©2012 Mladen Hruska This work is licensed under a Creative

Commons Attribution-ShareAlike 2.5 Canada License.Background image courtesy of [anankkml]/FreeDigitalPhotos.net

Analog Electronic Circuits

Lesson 1 – Introduction to Amplifiers



Outline

Amplifiers, where are they?

Ideal Amplifier

Practical Amplifier

Differential Amplifier

Cascading Amplifiers



Amplifiers, Where are they?

Obviously, Audio Amplifiers, Mobile Audio, Home Entertainment, Musical Instruments

EEG / ECG Machines

Radio Transmitters / Receivers

Process Instrumentation and Measurement

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Amplifiers, General Symbol



Ideal Amplifier

Linear Gain (Amplification)

Output = Input X A regardless of outside factors like change in temperature or supply voltage

Infinite Input Impedance (Zi)

No effect on the circuit it is connected to

Zero Output Impedance (Zo)

All power transferred to the Load

100% Efficient, no wasted power



Ideal Amplifier

Infinite Bandwidth

Output = Input x A at any frequency

Operates as an amplifier to an applied DC signal

Phase shift between input and output constant at any frequency

Cannot oscillate because of feedback



Gain (A)

Freq (Hz)Phase (º)

Freq (Hz)



Practical AmplifierLinear Gain (Amplification)

Design considerations minimize external effects using feedback, usually reducing per-stage Gain

Measurable Input Impedance (Zi)

Design “matches” or “bridges” impedance with signal source

Measurable Output Impedance (Zo)

Impedance depends on design, usually to maximize power to load or maximize efficiency

Biasing and Zo cause loss of efficiency



Practical Amplifier

Limited Bandwidth (Frequency Response)

Output varies according to input frequency

Coupling Capacitors limit low Hz response

“Stray” capacitance limit high Hz response

“Directly Coupled” amplifiers pass DC signal

Phase shift between input and output varies by frequency

Designed to avoid possibility of oscillation caused by phase shift and feedback



Gain (A)

Freq (Hz)Phase (º)

Freq (Hz)




Has two inputs labeled + -

Output amplified difference between inputs

Vo = A x (Vi+ - Vi-)

Does not amplify “common mode” signals

Vo = 0 where Vi+ = Vi-



Cascading Amplifier Stages

Difficult / Impossible to design a single stage amplifier that can provide high voltage and power gain with practical Zi and Zo while maintaining usable bandwidth

More economical to use several inexpensive transistors in design rather than a single expensive transistor

Amplifiers designed in “Stages” that progressively amplify the signal




First stage, impedance matching, high voltage gain, minimize / filter noise

Intermediate stage(s), further voltage gain

Current Gain stage

Power Stage




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Review

Amplifiers, where are they?

Ideal Amplifier

Practical Amplifier


Cascading Amplifiers



Credits and Attributions

Reference Texts:Boylestad, R.L., Nashelsky, L., (2009). Electronic Devices and Circuit Theory (10th ed.)

Floyd, T.L., (2012). Electronic Devices: conventional current version (9th ed.)

Images:All images as individually attributed courtesy of FreeDigitalPhotos.net users; anankkml, taoty, salvatore vuono, 9comeback, aopsan, rajcreationzs, jscreationzs listed in order of aperance.



Copyright (c) 2012 by Mladen Hruska. This work is made available under the terms of the Creative Commons Attribution-ShareAlike 2.5 Canada license

All images, diagrams, charts, etc. are the copyright work of Mladen Hruska if not immediately attributed otherwise

For more information: http://creativecommons.org/licenses/by-sa/2.5/ca/

http://creativecommons.org/licenses/by-sa/2.5/ca/

small signal amplifiers - lesson 1 - intro to amplifiers

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