What is Stagger Tuned Amplifier : Working Its Applications

An amplifier that amplifies an exact frequency or narrow band frequency is known as a tuned amplifier. This amplifier is mostly used to amplify the frequencies of high otherwise radio. These amplifiers provide an extremely high-impedance at the resonant frequency as well as extremely minute impedance at all other frequencies. Tuned amplifiers are classified into three types namely single tuned, double-tuned and stagger tuned amplifier. The advantages of these amplifiers mainly include power loss is less; selectivity is high, less harmonic distortion, radar, TV, RF amplifiers, etc. This article discusses an overview of the stagger tuned amplifier and its applications.

What is Stagger Tuned Amplifier?

Staggered tuned amplifier definition is an amplifier that is used to improve the total frequency response of the tuned amplifier. Usually, these amplifiers are designed to exhibit an overall response for maximal flatness in the region of the center frequency.

This amplifier uses tuned circuits to operate in union. The total frequency response of this amplifier can be achieved by adding up the separate response as one. When the different tuned circuit’s resonant frequencies are staggered otherwise displaced, then it is known as a stagger tuned amplifier.

Stagger Tuned Amplifier Working

The circuit diagram shown below is a two-stage stagger tuned amplifier. In this circuit, the stagger tuning can be achieved by producing the tuned circuits like L1C1 and L2C2 to a little different frequency. The stagger tuned amplifier circuit is shown below.

stagger-tuned-amplifier
stagger-tuned-amplifier

The double-tuned amplifier offers high BW like 3dB. However, the arrangement of this amplifier is not easy. So to conquer this difficulty two single tuned cascaded amplifiers are employed which have certain bandwidth. The resonant frequencies of BWs are adjusted and divided through an amount equivalent to the BW of every stage.

As these frequencies are staggered and called as stagger tuned amplifiers. The characteristics of these amplifiers are shown below. The following image shows the main relationship between individual stages amplification characteristics within a stagger tuned amplifier.

The amplifier using stagger tuning has greater BW, faster passband and number of stages used. The flatter will be the passband. The circuit is called stagger because the tuned circuit’s resonance frequencies are displaced.

stagger-tuned-amplifier-output-response
stagger-tuned-amplifier-output-response

The stagger tuned amplifier’s total frequency response is contrasted with the equivalent and separate single tuned stages. These stages include similar resonant circuits. In the following characteristics, the staggering decrease in the total amplification of the middle frequency to 0.5 of the crest amplification of the separation stage. At middle frequency, every stage includes 0.707 crest amplification of the separation stage. Therefore, the corresponding voltage amplification for each stage of the stagger will be 0.707 times higher when the two similar stages are utilized without staggering.

staggere-tuned-amplifier-characteristics
stagger-tuned-amplifier-characteristics

But, the 3dB BW of the stagger pair is √2 times higher than the BW of an individual single tuned stage. Therefore the corresponding gain BW product for each stage of stagger tuned pair can be 0.707 x √2 is equal to 1.00 times with the separate single tuned stages.

The thought of stagger tuned can be simply expanded to additional stages. In 3-stage staggering, the tuning of the primary circuit can be adjusted to a lower frequency than the center frequency. The 3rd circuit can be adjusted to high frequency compared with middle frequency. The tuned frequency which is in middle is adjusted at the precise center frequency.

Stagger Tuned Amplifier Derivation

The single tuned amplifier’s gain can be written as

Av/Av (resonance) = 1/ 1+2jQeff 𝛿

                                   = 1/1+jX

Where X = 2Qeff 𝛿

In a stagger tuned amplifier, the two amplifiers like single tuned cascaded are utilized with separate resonant frequencies. Assume that, if one stage of the amplifier is tuned with the frequency like fr + 𝛿 and another stage of the amplifier is tuned with the frequency like fr – 𝛿. Thus we have fr1 = fr + 𝛿 and fr2 = fr – 𝛿.

Based on the above two frequencies fr1 and fr2, the selectivity function can be written as

Av/Av (resonance)1 = 1/ j(X+1)
Av/Av (resonance)2 = 1/ j(X-1)

The total gain of these stages is equal to the product of two stages of individual gains

Av/Av (resonance) cascaded = Av/Av (resonance)1 * Av/Av (resonance)2

= 1/ j(X+1) * 1/ j(X-1)

= 1/ 2+2jX-X2 = 1/ (2-X2) + 2jX

|Av/Av (resonance) cascaded| = 1/√ (2-X2)2 + (2jX) 2

= 1/√ (4-4X2+X4+4X2) = 1/√4+X4

We know the value of X = 2Qeff 𝛿

Substitute this value in the above equation.

= 1/√4+(2Qeff 𝛿 )4

= 1/√4+16Q4eff 𝛿 4 = 1/2√1+4Q4eff 𝛿 4

Advantages and Disadvantages

The stagger tuned amplifier advantages & disadvantages include the following.

  • By using this amplifier an increased BW can be obtained. Compare with a single tune, the BW is √2 times.
  • This amplifier has a high value of gain BW.
  • In every stage of the amplifier, there is a small difference within the resonance. Therefore, enhanced stability within an operation can be obtained.
  • The bandpass of this amplifier is faster compare with a single tuned amplifier. The alignment of this circuit is easy when we compare it with the single tuned amplifier.

Applications

The stagger tuned amplifier applications include the following.

  • It is used in a superheterodyne receiver as an IF (intermediate frequency) amplifier
  • It is used in UHF radio relay systems.
  • It is extremely narrow-band intermediate frequency amplifier within a spectrum analyzer
  • It is used like a wideband tuned amplifier intended for Y-amplifiers within oscilloscopes;
  • It is used for video amplification like a wideband tuned amplifier.
  • It is used like RF amplifiers within receivers
  • IF amplifier in a satellite transponder

Thus, this is all about Stagger tuned amplifier. From the above information finally, we can conclude that these amplifiers are usually designed so that the total frequency response exhibits maximum flatness approximately the middle frequency. It requires several tuned circuits to operate in combination. Once the frequency is changed above & below the resonant frequency, then it falls off quickly.

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