Most of the electronic systems require at least one stage of amplification. Hence amplifiers can be seen in almost all the electronic devices. Amplifiers are the devices that increase the amplitude of the input signal.
The output of the power supply is modulated by the Amplifier. Amplifiers increase only the amplitude and the other parameters such as frequency and shape remain constant.
There are many types of amplifiers available. But they can be distinguished by the type of signal they amplify. They can also be classified by the type of function they perform.
There are three categories of amplifiers depending on the property of their output.
- Voltage Amplifier
- Current Amplifier
- Power Amplifier
Let us know discuss about these amplifiers in detailed manner.
- 1. Voltage Amplifiers:
- 2. Current Amplifiers:
- 3. Power Amplifiers:
- 1. Audio Frequency Amplifiers (A.F. Amplifiers):
- 2. Intermediate Frequency Amplifiers (I.F. Amplifiers):
- 3. Radio Frequency Amplifiers (R.F. Amplifiers):
- 4. Ultrasonic Amplifiers:
- 5. Wideband Amplifiers:
- 6. Direct Coupled Amplifiers (DC Amplifiers):
- 7. Video Amplifiers:
- 8. Buffer Amplifiers:
1. Voltage Amplifiers:
These are most common amplifiers used in the electronic devices. These amplifiers increase the amplitude of the output voltage of the signal.
2. Current Amplifiers:
These amplifiers increases the amplitude of the input current compared to the input current waveform.
3. Power Amplifiers:
The purpose of the power amplifiers is to increase the power i.e. the product of output voltage and current is greater than the product of input voltage and current.
Either the voltage or current at the output may be less than the input, the overall voltage or current product will be greater than the input. When an AC signal is applied to the amplifier, only a part of it is amplified.
Depending on the portion of wave amplified, these are classified into four classes. They are
- Class A
- Class B
- Class AB
- Class C
Amplifies can be further classified based on the signal they amplify. They are as follows:
1. Audio Frequency Amplifiers (A.F. Amplifiers):
Audio Frequency Amplifiers amplify the audio frequencies. Generally audio frequencies are in the range of 20 Hz to 20 kHz. Some of the HI-FI audio amplifiers may amplify up to 100 kHz.
These are used to supply audio frequency power to operate the loud speakers. Most of the modern audio amplifiers are based on solid state dives such as transistors, in early stages they are made of vacuum tubes.
2. Intermediate Frequency Amplifiers (I.F. Amplifiers):
Intermediate frequencies are amplified by this amplifier. These amplifiers are used in TV, radio and radar. They provide the maximum voltage amplification of a radio, TV or radar signal, before the video or audio information carried by the signal is demodulated.
Their frequency of operation is lower than that of the received radio signal, but higher than the audio or video signals eventually produced by the system. The type of equipment decides the frequency at which I.F. amplifiers operate.
3. Radio Frequency Amplifiers (R.F. Amplifiers):
This amplifier increases the power of low-frequency radio signal. These are used to drive antenna of a transmitter. Radio Frequency amplifiers are tuned amplifiers whose the frequency of operation is controlled by the tuned circuit. This circuit can be adjusted depending on the amplifier purpose. Input resistance is generally low, as is gain.
A special feature of RF amplifiers is low noise performance. So they are used in the earliest stages of a receiver. The background noise generally produced by any electronic device is kept to a low value as the amplifier handles very low amplitude signals from the antenna. Hence low noise FET transistors used in these stages.
4. Ultrasonic Amplifiers:
Ultrasonic amplifiers amplify the ultrasonic waves. These are in the frequency range of around 20 kHz up to about 100 kHz. They are used for specific purposes such as ultrasonic cleaning, ultrasound scanning, remote control systems etc. Each type will operate at narrow band of frequencies within the ultrasonic range.
5. Wideband Amplifiers:
Wideband amplifiers will amplify a band of frequencies. They amplify from DC to several tens of MHz They are used in equipment such as oscilloscopes etc. These are used where there is a need to accurately measure signals over a wide range of frequencies. Because of their wide bandwidth, gain is low.
6. Direct Coupled Amplifiers (DC Amplifiers):
Direct coupled or DC amplifiers are used to amplify very low frequency signals. The output of one stage is coupled with the input of the next stage in these amplifiers. This amplifier amplifies the DC frequency that is zero frequency. They are mostly used in many electrical control systems and measuring instruments.
7. Video Amplifiers:
Video amplifiers are used to improve the video signal and display it with high resolution. The video signal carries all the information about picture in TV and radar systems. They are a special type of wide band amplifier. They are used specifically for signals that are to be applied to video equipment.
The bandwidth of video amplifiers depends on use. In TV receivers they extend from 0Hz to 6MHz and is still wider in radar. These amplifiers are used to amplify the signals received from DVDs, computer monitors. They can also be used to amplify the video quality in small TVs that are installed in the vehicles.
8. Buffer Amplifiers:
Buffer amplifiers are commonly used to for electrical impedance transformation from one circuit to another. They have amplifier gain of 1.They are used for isolating the circuits from each other. They have high impedance at the input and low impedance at the output .
Therefore can be used as impedance matching device. This implies that signals are not attenuated between circuits, which happens when a circuit with high output impedance feeds a signal directly to another circuit having a low input impedance.
9. Operational Amplifiers:
Operational amplifiers are high gain electronic voltage amplifiers. The operational amplifiers are used to perform mathematical operations on voltages . They are used in the form of ICs initially they were developed with the vacuum tubes. The operational amplifier has two input terminal mainly.
They are inverting and non-inverting. They can be used as inverting amplifiers, non-inverting amplifiers, summing amplifiers, difference amplifier etc. The following figure shows the operational amplifier.
Related Post: Function Generator using Operational Amplifier
10. Transistor Amplifiers:
Transistor is an electronic device. This is also used as an amplifier. Transistor amplifiers amplify the voltage or current of the input signal.
There are two types of transistor devices. 1) BJT (Bipolar junction transistors). 2) FET(Field Effect Transistors).
Transistor amplifiers are analyzed in different configurations. They are 1) Common Base, 2) Common Emitter and 3) Common Collector using BJT. By using FET, transistor amplifiers are analyzed in the following configurations. 1) Common Gate, 2) Common Source and 3) Common Drain.
In Bipolar Junction Transistors, small current at the terminal of base can control the current at emitter and collector, while in Field Effect Transistors (FET) small voltage at the gate can control the voltage at source and drain.