A tuned RF amplifier is a type of radio frequency amplifier that selectively amplifies a narrow range of radio frequencies from a wide frequency spectrum. This amplifier employs a tuned LC tank circuit in the place of its load. This tuned circuit is capable of selecting a narrow band of desired frequencies while rejecting all others. This process of selecting a specific narrow range of frequencies from a broad frequency spectrum is called as tuning.
Working of a Tuned RF Amplifier
The resonant frequency of an LC circuit is the frequency at which the reactance of the inductor balances with the reactance of the capacitor. It is denoted by Fr.
A parallel tuned radio frequency amplifier offers high impedance at the resonant frequency, and does not allow much current through it. It offers low impedance to all other frequencies away from the resonant frequency.
The tuned radio frequency amplifier offers high impedance at resonance that allows signals at the desired frequency, but offers low impedance to frequencies above or below the resonant frequency, thus rejecting signals in those frequencies. Thus a tuned amplifier selectively amplifies the desired signals and rejects all other signals.
The formula for calculating the resonant frequency of the amplifier is
Fr = 1/2π√LC
The Q factor or the sharpness of the resonance curve of the LC tuned circuit of the amplifier determines the selectivity of that circuit. The Q factor of a resonant circuit is dependent on the internal resistance of the inductor (L) of the circuit. The lower the resistance of the inductor, the higher the Q factor.
Tuned Radio Frequency Amplifier Circuit
Advantages of Tuned RF Amplifiers
1# The use of reactive components in a tuned radio frequency amplifier such as the inductor and the capacitor reduces the power loss at resonant frequency due to the high impedance which makes it efficient. Thus a smaller collector supply voltage is necessary.
2# The selectivity and amplification of the desired radio frequency signal is high in tuned radio frequency amplifiers.
Applications of a Tuned Radio Frequency amplifier
- A tuned RF amplifier is used as a front-end radio frequency amplifier in radio, television and communication receivers.
- It is used as a tuned Intermediate frequency amplifier in radio, TV and communication receivers.
- Tuned amplifier is used as a selective RF amplifier to amplify only the desired signals in transceivers and transmitters.
- RF power amplifiers utilize tuned RF amplifiers to amplify the required signals before they are being transmitted through the antenna.
- Tuned amplifiers are used in frequency converters and doublers to selectively amplify the required signals while rejecting all others.
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