                            Amplifier Teaching Aid (GTZ, DED; 86 pages)  Preface  Introduction  Lesson 1 - Semiconductor Review  Lesson 2 - Bipolar Transistor  Bipolar Transistor II  First Evaluation  Lesson 4 - Transistor Fundamentals  Lesson 5 - Transistor Biasing  Lesson 6 - Transistor Biasing II  Second Evaluation  Lesson 7 - Small Signal Amplifier  Lesson 8 - Small Signal Amplifier II   Lesson Plan    Signals in a CE amplifier    Input impedance    Impedance matching   Handout No. 1   Worksheet No. 8  Lesson 9 - Small Signal Amplifier III  Lesson 10 - Large Signal Amplifier  Third 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   