In many applications, it is required to amplify the signals with minimum distortions. For that, we need to use amplifiers for the amplification of signals. In this lecture, we are going to learn about the classification of Amplifiers based on various factors.
Classification of Amplifiers:
Amplifiers can be classified based on the various factors as follows:
- Classification based on the purpose of amplification
- Classification based on the frequency range
- Classification based on the position of Q Point
- Classification based on the type of coupling
1.Classification based on the purpose of Amplification:
Voltage Amplifiers :
- The amplifiers can be classified broadly as voltage amplifiers and power amplifiers.
- Voltage amplifiers are supposed to amplify the voltage i.e. to amplify weak voltage signals.
- However, these are not capable to supplying a large power to the load. The voltage amplifiers can be used as intermediate stages in a public address (P.A.) system as shown in the figure.
- To deliver a large power to the load, a specially designed amplifier called as “Power Amplifier” is used as the final stage as shown in the figure.
- It is called as the “Large Signal Amplifier” because it is capable of supplying an adequately large amount of power to the loads like a loudspeaker.
- The primary aim of a power amplifier is to supply a large power therefore the voltage gain is not important. Power amplifiers are used as the last stage in the P.A system, radio receivers, TV receivers etc.
Some of the important features of power amplifiers are as follows:
- Impedance matching with the load is necessary for maximum transfer or power.
- They use power transistors.
- Power amplifiers are bulky due to the use of heat sinks.
- Harmonic distortions are present in the output.
- They are capable of handling a large power.
2.Classification based on the Frequency Range:
Another way of classifying the amplifiers is depending on the frequency range of the input signal which is to be amplified. Depending on the frequency range, we can classify the amplifiers as:
- Audio frequency (AF) amplifiers
- Radio frequency (RF) amplifiers
- Wide-band amplifiers
Audio frequency (AF) Amplifiers:
- These amplifiers are designed to amplify the signal in the audio frequency range i.e 20Hz to 20 Khz.
- The transistors used in the AF amplifiers are called as AF transistors. AF amplifiers are used n the radio-TV, tape recorders, P.A. systems etc.
Radio frequency (RF) Amplifiers:
- The range of frequencies extending from 300 kHz to 30 MHz is called as “radio frequency range”. The amplifiers which are designed to operate in this frequency range are called as RF amplifiers.
- These amplifiers are also known as tuned amplifiers because a parallel LC circuit is used as a load for them. RF amplifiers are used in radio and TV receivers.
- These amplifiers have a very large bandwidth. typically a few MHz. Therefore they are called as wideband amplifiers.
- The video amplifiers used in TV receivers and VCR are wideband amplifiers having a bandwidth of about 5 MHz.
- These amplifiers are capable of amplifying the signals from about 10 Hz to 5 MHz.
3.Classification based on the type of Coupling:
- In the multistage amplifiers, the output signal of the preceding stage is to be connected to the input of the next stage.
- This is called as interstage coupling. The interstage coupling can be achieved by using any one of the following coupling techniques.
- The amplifiers are classified based on the type of couplings as:
- R-C coupling
- Transformer coupling
- Direct coupling
4.Classification based on the Position of Q Point:
- Depending on the position of the Q-point or operating point on the load line, the amplifiers are classified into the following four categories:
- This classification has been done on the basis of the position of the Q-point on the load line.
- The type of amplifier and the position of the Q-point are listed in below table:
|Sr. No||Type of Amplifier||Position of Q-point|
|1.||Class -A||At the center of the load line|
|2.||Class – B||In the cutoff region|
|3.||Class – AB||Just above the cutoff|
|4.||Class – C||Below the cutoff|
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