Feedback - Ch Chapter 8: Feedback Fall 2010 EE EE 230:...

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Chapter 8: Feedback Fall 2010 E 230: Electronic Circuits and EE 230: Electronic Circuits and Systems imothy A Bigelow Timothy A. Bigelow 1
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Advantages of Negative Feedback esensitize the Gain Desensitize the Gain Make value of gain less sensitive to variations in the value of circuit components, such as might be caused by changes in temperature. Extend the Bandwidth ontrol the put/Output pedances Control the Input/Output Impedances Raise or lower input or output impedances by appropriate selection of feedback topology. Reduce the Effect of Noise Minimize the contribution to the output of unwanted electric signals. 2
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Review of Op-Amp Feedback Op-Amp Gain  1 o p A As s 1 1 s f s f s R R RR R   Feedback Factor ff Transfer Function 1 o oo o g o A Av A vv v H s  3     1 1 1 og pg p o s sv A 
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Feedback: Exchange Gain for Bandwidth!   1 o p A As s 4 Modified from Microelectronic Circuits - Fifth Edition Sedra/Smith
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Review Basics of Negative Feedback     yt x t  s xt o A(s) + Source   i Load - (s)   f 5
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Review Basics of Negative Feedback 6
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Review Basics of Negative Feedback Feedback Factor L o o p G a i n   1 AL A Amount of Feedback  o f x A AC l o s e d L o o p G a i n A  1 1 Gain Determined by Feedback A  1 s xA 7
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Desensitize the Gain 1 f A A A 8
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Bandwidth Extension 1 o A s s      1 1 p f o As A s A s 1 p o A 1 11 oo o A A ss A   9   1 p op A 
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Basic Topologies: Voltage Amplifiers R s + - + v out + - v v s R L Basic Voltage Amplifier - Feedback Network 10
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Series-Shunt (Voltage) Feedback Amplifier: Ideal Case R + - + v o v s R i Av i + - + v i o - + - v f - + + - v o v o - 11
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Series-Shunt Feedback: Ideal Case – Input Impedance 12
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Series-Shunt Feedback: Ideal Case – Output Impedance 13
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Series-Shunt Feedback: Ideal Case – Output Impedance 14
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Properties of Voltage Amplifier w/ Feedback Also called – SERIES-SHUNT FEEDBACK Feedback increases input impedance Feedback decreases output impedance 15 Voltage Amplifiers have HIGH input impedance and LOW output impedance !
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Basic Topologies: Current Amplifiers i out i s R L Basic Current Amplifier R s i f i i out Feedback f Network 16
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Shunt-Series (Current) Feedback Amplifier: Ideal Case i i i o i s R i Ai i R o i f i i o f i o 17
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This note was uploaded on 10/16/2010 for the course EE 201 taught by Professor Kruempel during the Spring '06 term at Iowa State.

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Feedback - Ch Chapter 8: Feedback Fall 2010 EE EE 230:...

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