What is Tuned Amplifier : Working and Its Applications

As we know that there are many advantages of using amplifiers. We can amplify or boost the signal without changing any information of the signal. This can be done by using various types of amplifiers. Amplifiers are classified based on the input and output parameters like voltage amplifiers, current amplifiers, and power amplifiers. But in those amplifiers, tuned amplifiers are unique. By the end of this article, we will discuss what is tuned amplifier, circuit diagram with working, different types, applications, and advantages.

What is a Tuned Amplifier?

These amplifiers are one kind of amplifier that selects the particular range of frequencies and rejects the undesired frequencies by employing a tuned circuit at its load. The selective range of frequencies can be amplified by using these amplifiers. We can define the tuned circuit in different ways. These are helpful to amplify the higher frequencies or radio frequencies.

These amplifiers include the tuned circuits at its load part to select the desired frequencies. Tuning can be done by a tuned circuit. Tuning means selecting particular frequencies. The tuning circuit can be built with various components like inductor (L) and capacitor (C). The parallel combination of the inductor and capacitor is called a tuned circuit. Tuned circuit efficiency defines the performance of this amplifier. Below figure 1 shows the basic diagram of an amplifier circuit. And figure 2 shows the tuned circuit diagram.

Tuned Amplifier Circuit

The above figure 1 represents the circuit diagram. In this circuit, at the end of the collector terminal, a tuned circuit can be placed to select the particular range of frequency and need to reject the other frequencies efficiently. At the end of this circuit, the desired frequency oscillations will come as output.

“The frequency at which the inductor reactance value equals to the capacitors reactance value, such frequency is called resonant frequency, and it is indicated by Fr”

Frequency Range

Figure 2 is the circuit diagram of the tuned circuit. According to that, the resonant frequency ‘Fr’ and impedance of the tuned circuit is

Fr=1/2π√LC

Zr = L/C.R

The below graph shows the response between frequencies to the gain of the amplifier. We can say like the tuned amplifier frequency range. At resonant frequency ‘Fr’, the gain of this amplifier is large. The gain will be reduced below the resonant frequency & after the values of the resonant frequency. The gain will not maintain the highest value on these frequencies. In the frequency range of the amplifier diagram, 3dB range is indicated by ‘B‘ and 30dB range is indicated by the S. Therefore the ratio between B to S is called skirt selectivity. At Fr, this amplifier is resistive and cosФ= 1. It indicates the voltage and current both are in the same phase.

Types of Tuned Amplifiers

These amplifiers mainly have three types. They are

• Single tuned
• Double tuned
• Stagger tuned

Now, will discuss the description of types of these amplifiers. Let’s start with the first model.

Single Tuned Amplifier

These amplifiers are classified based on the number of tuned circuits used in the tuned amplifier. If the amplifier has only one tuned circuit then it is called a single tuned amplifier. This amplifier has only one tuned circuit at the collector terminal of the amplifier. The resonant frequency of this amplifier is Fr=1/2π, where L and C are the inductor and capacitors of the amplifier. If this amplifier has low bandwidth then it’s not able to amplify the complete signal equally. And this results in the reproduction process. This indicates the stability of the amplifier.

Double Tuned Amplifier

These types of amplifiers include two tuned circuits. Each amplifier has a tuned circuit at the end of the collector terminal. And the first and second amplifiers are coupled with an inductor. Because of the two tuned circuits, a sharp response will get at the output. And it offers a larger 3 dB bandwidth than the single tuned. Both circuits are tuned to the same frequency. By properly adjusting the L1 and C1 of the first tuned circuit, L2 and C2 of the second tuned circuit the output will be taken at output ports of the double-tuned amplifier.

The high-frequency signal is applied at the input port of the amplifier. So the input needs to amplify with the help of the double-tuned. Whenever the first amplifier is tuned to the input signal frequency, then the output is forwarded to the second stage of the amplifier through L2 and C2. At this stage, the first amplifier offers high reactance to the signal frequency. Whenever the second stage amplifier gets the input from L1 and C1 it also tuned to its frequency and delivers the amplified output at the output port of the double-tuned. It provides a larger 3dB bandwidth than the single tuned. And provides high gain-bandwidth value.

Stagger Tuned Amplifier

These amplifiers are useful to amplify the signal for a particular frequency range only. And we get more frequency bandwidth in double-tuned than the single tuned.  But there is a complex process in the alignment of the double-tuned. So to overcome this amplifier like stagger tuned ” is introduced.

This amplifier is a cascading of single tuned amplifiers. These amplifiers were in cascade form which is having a certain bandwidth and their resonant frequencies set to equal bandwidth of each stage. This type of amplifier gives more bandwidth. The need for a stagger tuned is, the double stage amplifier gives more bandwidth but alignment is a complex process. These amplifiers are introduced to make easier & to get flat bandwidth. The main advantage of the stagger tuned is it has a flat, better and wide frequency characteristic. The below figure shows the bandwidth area coverage of amplifiers like a single tuned and staggers tuned.

Advantages

The advantages of this amplifier include the following.

• There is a minimum power loss in tuned circuits because in the tuned circuit they use only inductor and capacitor reactive components.
• It provides high selectivity.
• SNR at the output level is good.

Applications

The applications of this amplifier include the following.

• These amplifiers are used to select a particular range of frequencies like in dish, radio, etc.
• These amplifiers are used to amplify the desired signal to a high level.
• These amplifiers are preferable in wireless communication systems.
• Radio and television broadcastings are very helpful to select a particular range of frequencies.

Thus, by using these amplifiers, we can increase the amplitude level at higher frequencies. And also we can select the desired frequency range to amplify it and to avoid the unwanted frequency range by using these amplifiers. Here is a question for you, what are the disadvantages of tuned amplifiers?