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Unformatted text preview: ecture 27 Lecture 27 Amplifier Configurations Reading: CE/CS: Jaeger 13.6, 13.9, 13.10, 13.11 CC/CD: Jaeger 14.1, 14.3 B/CG: Jaeger 14 1 14 4 CB/CG: Jaeger 14.1, 14.4 and Notes ECE 3040  Dr. Alan Doolittle Georgia Tech Amplifier Configurations Voltage Amplifier: Voltage input and Voltage output ifier Input sistance rce Input sistance Resistance fier Output sistance Ampli Res Sour Res Load R Amplif Res Source Load Amplifier • Any signal source has a finite “source resistance”, R S . • The amplifier is often asked to drive current into a load of finite The controlled source is a VoltagecontrolledVoltage Source impedance, R L (examples: 8 ohm speaker, 50 ohm transmission line, etc…) ECE 3040  Dr. Alan Doolittle Georgia Tech A v =Open Circuit Voltage Gain can be found by applying a voltage source with R s =0, and measuring the open circuit output voltage(no load or R L =infinity) Amplifier Configurations Why is the input and output resistance important? •Only the voltage v in is amplified to A v v in . •Since R s and R in form a voltage divider that determines v in , you want R in as rge as possible (for a voltage amplifier) for maximum voltage gain. large as possible (for a voltage amplifier) for maximum voltage gain. •Since R L and R out form a voltage divider that determines v out , you want R out as small as possible (for a voltage amplifier) for maximum voltage gain. ECE 3040  Dr. Alan Doolittle Georgia Tech Amplifier Configurations Current Amplifier: Current input and Current output he controlled source is a Current ntrolled urrent Source The controlled source is a Current controlled Current Source A i =Short Circuit Current Gain can be found by applying a current source with R s = infinity, and measuring the short circuit output rrent (No Load or R 0) current (No Load or R L =0) •Only the current i in is amplified to A i i in . •Since R s and R in form a current divider that determines i in , you want R in as small as ibl (f t lifi ) f i t i ECE 3040  Dr. Alan Doolittle Georgia Tech possible (for a current amplifier) for maximum current gain. •Since R L and R out form a current divider that determines i out , you want R out as large as possible (for a current amplifier) for maximum current gain. Amplifier Configurations Transconductance Amplifier: Voltage input and Current output The controlled source is a VoltagecontrolledCurrent Source G m =Transconductance Gain can be found by applying a voltage source with R s =0, and measuring the short circuit output current o Load or R =0) (No Load or R L 0) •Only the voltage v in is amplified to i out =G m v in . •Since R s and R in form a voltage divider that determines v in , you want R in as large as ossible for maximum transconductance gain ECE 3040  Dr. Alan Doolittle Georgia Tech possible for maximum transconductance gain....
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This note was uploaded on 08/23/2011 for the course ECE 3040 taught by Professor Doolittle during the Spring '11 term at University of Florida.
 Spring '11
 Doolittle
 Amplifier

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