What is Voltage Amplifier and Current Amplifier?
Voltage Amplifier :-
A voltage amplifier is an amplifier that meets the demand for how much power it will receive in a circuit and how much input or output voltage it will require in that circuit.
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A voltage amplifier is required to amplify signal voltage in situations where the power consumed by the load impedance is not of prime concern.
The amplifiers in the pre-amplifying stage of a radio receiver are voltage amplifiers.
Each such amplifier gives at its output an amplified voltage that serves as the input of the next stage.
A power amplifier, on the other hand, seeks to supply power to a load such as a loudspeaker or a radio antenna.
Thus power amplifiers constitute the last stage of a radio receiver feeding the loudspeaker, or the last stage of a transmitter connected to the transmitting antenna.
An ideal voltage amplifier is one for which the proportionality factor between the output voltage and the input voltage (the voltage gain) is independent of the signal amplitude and frequency , which introduces no noise and distortion of the signal, and which has an infinite input resistance and zero output resistance.
The infinite input resistance implies that the voltage gain does not depend on the resistance of the input signal source.
The zero output resistance ensures that the voltage gain is independent of the load resistance. Practical voltage amplifiers do not fulfill these requirements.
Current Amplifier :-
A current amplifier is an amplifier that meets the demand for how much power it will receive in a circuit and how much input or output current it will require in that circuit.
An ideal current amplifier is defined as an amplifier for which the proportionality factor between the output current and the input signal current (the current gain ) is independent
of the signal amplitude and frequency , which do not introduce any noise and distortion of the signal , and which has zero input resistance and infinite output resistence.
Since the input resistence is zero, the current gain is independent of the source resistence and since the output resistence is infinite, the current gain is independent of the load resistence.
Practical current amplifiers do not meet these requirements.
Frequency Amplifier :
An frequency amplifier means to amplify any frequency like audio, video and radio.
And this amplifier are divided into three parts -
- Audio frequency amplifier.
- Video frequency amplifier.
- Radio frequency amplifier.
1. Audio frequency amplifier :
An amplifier means to amplify audio frequency (about 20Hz to 20kHz ) signals is referred to as an audio frequency (abbreviated AF) amplifier. AF amplifier are used in sound systems.
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| Audio frequency amplifier |
2. Video frequency amplifier :
An amplifier designed to amplify signals over a wide band of frequencies is known as a video or a broadband amplifier.
Such amplifiers are employed in TV to amplify picture signals having frequencies up to above 4.5 MHz.
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| Video frequency amplifier |
Since audio and video amplifiers do not use tuned circuits, they are known as untuned amplifiers.
3. Radio frequency amplifier :
The amplifiers designed to amplify signals over a certain range of frequencies in the radio frequency range ( about 20 kHz to 30 MHz ) and reject others, are termed radio frequency (abbreviated RF) amplifiers.
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| Radio frequency amplifier |
The RF amplifier in the first stage of a radio receiver amplifies a narrow band of frequencies about the carrier frequency.
Unlike audio and video amplifiers, RF amplifiers employ tuned circuits and are therefore also known as tuned amplifiers.
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