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 Plan Small signal amplifier Coupling capacitor Bypass capacitor Amplifier analyzing method Worksheet No. 7 Experiment No. 4 Lesson 8 - Small Signal Amplifier II Lesson 9 - Small Signal Amplifier III Lesson 10 - Large Signal Amplifier Third Evaluation

#### Coupling capacitor

A capacitor is open at low frequencies and shorted at high frequencies.

Capacitive reactance (XC) is inversely proportional to frequency (f) and to capacitance (C). For a coupling capacitor to work properly, it has to act like an ac short at the lowest frequency that the ac source can have. To realize that we can use the following rule:

XC < 10 R
Make the reactance at least 10 times smaller than the total resistance in series with the capacitor.

Ex: Calculate the capacitance of C1 for a proper ac transmittance. Frequency range: 20-20000 Hz

Fig. 7-1: Use of coupling capacitor

Total resistance: 1KΩ + 500Ω = 1.5KΩ

XC <= 10 * R -- >

-- >

C = 53μF

The capacitor to choose should be bigger than 53μF. The next standard value is:

C = 56μF