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close this bookAmplifier Teaching Aid (GTZ, DED; 86 pages)
View the documentPreface
View the documentIntroduction
Open this folder and view contentsLesson 1 - Semiconductor Review
Open this folder and view contentsLesson 2 - Bipolar Transistor
Open this folder and view contentsBipolar Transistor II
View the documentFirst Evaluation
Open this folder and view contentsLesson 4 - Transistor Fundamentals
Open this folder and view contentsLesson 5 - Transistor Biasing
Open this folder and view contentsLesson 6 - Transistor Biasing II
View the documentSecond Evaluation
Open this folder and view contentsLesson 7 - Small Signal Amplifier
close this folderLesson 8 - Small Signal Amplifier II
close this folderLesson Plan
View the documentSignals in a CE amplifier
View the documentInput impedance
View the documentImpedance matching
View the documentHandout No. 1
View the documentWorksheet No. 8
Open this folder and view contentsLesson 9 - Small Signal Amplifier III
Open this folder and view contentsLesson 10 - Large Signal Amplifier
View the documentThird Evaluation
 

Impedance matching

When you couple some amplifier stages or connect electronic appliances, the input/output impedance of every stage will effect the efficiency.


Fig. 8-2: Impedance matching

The internal resistance/impedance of the signal source (R1) and the loudspeaker (R4) is fixed. Only R2 and R3 can be designed to match the impedance.

Voltage optimum

Between signal source and amplifier it is important to transfer the highest possible voltage.


Fig. 8-3: Voltage optimum

In order to get the highest, possible voltage (V2) let's try several values for R2.

Ex: V = 10V, R1 = 100 Ω

R2 = 0.1 * R1 --- >


R2 = R1 --- >


R2 = 10 * R1 --- >


R2 = 100 * R1 --- >

The input impedance of an amplifier should be much bigger than the internal resistance of the signal source.

Power Optimum

Between amplifier and loudspeaker it is most important to transfer the highest possible power.


Fig. 8-4: Power optimum

Ex: Power in the load under different values of R4.

V = 10V, R3 = 8Ω

PL = R4 * I2

R4 = 16Ω

I = 24Ω = 0.42A

PL = 2.78W

     

R4 = 8Ω

I = 16Ω = 0.63A

PL = 3.125W

     

R4 = 4Ω

I = 12Ω = 1.14A

PL = 1 .03W

Input impedance of the load and the output impedance of the amplifier should have the same value.

R3 = R4

Ri = RL

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