What you are expected to learn

At the end of this module, you should be able to:

• Describe the purpose of an amplifier.
• Identify the three basic configurations of transistor amplifier circuits.
• Identify the classes of amplifiers.
• Describe the operation of direct coupled amplifiers, audio amplifiers, video amplifiers, RF amplifiers, IF amplifiers, and operational amplifiers.
• Draw and label schematic diagrams for the different types of amplifier circuits.

How to learn from this module

Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some

tips for you:

1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.

2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.

3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.

4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.

5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.

What to do before (Pretest)

• Amplifiers are electronic circuits used to increase the amplitude of an electronic signal.
• The transistor is used primarily as an amplifying device.
• The three transistor amplifier configurations are common base, common collector, and common emitter.
• Common-collector amplifiers are used for impedance matching.
• Common-emitter amplifiers provide phase reversal of the input-output signal.
• All transistor amplifiers require two voltages for proper biasing.
• A single voltage source can provide the necessary forward-bias and reverse-bias voltages using a voltage-divider arrangement.
• A voltage-divider feedback arrangement is the most commonly used biasing arrangement.
• A transistor amplifier can be biased so that all or part of the input signal is present at the output.
• Class A amplifiers are biased so that the output current flows throughout the cycle.
• Class AB amplifiers are biased so that the output current flows for less than the full but more than half of the input cycle.
• Class B amplifiers are biased so that the output current flows for only half of the input cycle.
• Class C amplifiers are biased so that the output current flows for less than half of the input cycle.
• Coupling methods used to connect one transistor to another include resistance capacitance coupling, impedance coupling, transformer coupling, and direct coupling.
• Direct-coupled amplifiers are used for high gain at low frequencies or amplification of a DC signal.

Self Check

1. Briefly describe how a transistor is used to provide amplification.

2. Why is the common-emitter amplifier the most widely used transistor amplifier configuration?

3. What factor affects the gain of the transistor, and what must be done to compensate for it?

4. How does an amplifier’s class of operation affect the biasing of the amplifier?

5. What factor must be taken into consideration when connecting one amplifier to another?

6. How does the frequency of operation of an amplifier affect the coupling method used in connecting amplifiers together?