Feedback Amplifier Transistor Oscillator

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Principle of Operation of Oscillator

Electronic devices function on a tank circuit to enable the sharing of information, generally, an amplifier with a sinusoidal input attains an amplified output signal. In a feedback amplifier and transistor oscillator, the oscillator generates an amplified output signal without any intake of input signals. The working of an oscillator is a repetitive process with the amplified input and output resulting in feedback with persistent operations. This ensures the transmission of information signal back and forth in an electronic device without any interval. 

This infers a single input lead with endless outputs based on the feedback and frequency regulated, the external signal delivers an alternating current which is self-sustainable.

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Types of Feedback Amplifiers

In the working of an oscillator, feedback refers to the ability of the output signal to return to the input. There are 2 types of feedback amplifiers:

1. Positive Feedback Amplifier

As shown in the image, Vin is the input signal sourced through the transistor to Vout is the output, further, the succeeding network formed with the sourcing of Vout back to Vin is positive feedback indicated with Vf in the figure. These positive feedback amplifiers are utilized for oscillations. 


2. Negative Feedback Amplifier

On the contrary, a negative feedback amplifier indicates the incapacity of the (Vout) output signal to return to the (Vin) input signal.


Types of Transistor Oscillators and Functions

Let's quickly take a look at some types of transistor oscillators and how they function.

1. Working of Colpitts oscillator

A variation of an oscillator tank circuit formed with 2 capacitors and 1 inductor. Its connectivity can be achieved in series allowing the inductor to be placed in a parallel position to the capacitors.

The working of the Colpitt oscillator was invented in 1918 and named after scientist Edwin Colpitts. As compared to the working principle of the Hartley oscillator, it stimulates preferable frequency stability.


2. Working principle of Hartley Oscillator

Hartley Oscillator is a tank circuit composing 2 inductors and one capacitor. The inductors are linked in combining series whereas the capacitor is positioned parallel to the series of inductors. Discovered in the year 1915 and named after an American scientist Ralph Hartley. It generally operates with frequencies ranging from 20 kHz to 20MHz.


3. Working of Wien Bridge Oscillator

Wein bridge oscillator is a bridge circuit formed with 4 resistors and 2 capacitors. It produces sine waves with largely ranging frequencies. Working of Wien bridge oscillator was formulated and named after Max Wein in the year 1891 for measuring impedances. 

Now that we have analyzed and understood the functioning of feedback amplifier and transistor oscillator, we've comprehended the functioning of varied oscillations like the working of Colpitts oscillator, working principle of Hartley oscillator, and working of Wien bridge oscillator. 

One of the factors that remain constant is the positive feedback gained to achieve repetitively and long-term processing of signals. You can also avail notes in pdf formats on our website or the Vedantu app covering feedback amplifier and transistor oscillator and other relevant topics to make learning an effortless task resulting in optimum grades.


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Solved Example

In an Oscillator Working Principle, What is Positive Feedback?

Answer- Positive feedback adopted in the working of an oscillator stimulates an output frequency without the implementation of any input. Positive feedback boosts the output signal by charging a quicker and higher signal in the direction of the input. It functions in a loop permitting continuous and undamped oscillations. Following the principle 'more produces more' it is utilized in procedures like fruit ripening and contractions in childbirth. Amplification in an oscillator only administers with positive feedback as it feeds the output signal back to the input to model it to be in phase, further the feedback and input enhance the amplifier.


Did You Know?

  • A classic based on feedback control theories published in 1868 was the first-ever written theory relating to feedback by James Clerk Maxwell as a popular paper named 'On governors'.

  • The verbal application of the word 'feedback' was implemented in the US in the 1860s, however, the official usage of the word 'feedback' as a noun was witnessed in the year 1909 by Nobel laureate Karl Ferdinand Braun referring to bonding of the elements in an electronic circuit.

FAQ (Frequently Asked Questions)

Working Principle of the Hartley Oscillator Is Most Commonly Utilized in ________?

  1. TV Receivers

  2. Radio Receivers

  3. Radio Transmitters

  4. None of the above 

The answer to the question would be option B: Radio Receivers.

Explanation: The Hartley Oscillator layout with a tank tuned circuit has a Radio Frequency coil with sustaining fractions of signal from the output to the transistors, it enhances the execution of the radio receivers with transitions in frequency. Hartley oscillators are generally used in superheterodyne receivers like a radio receiver and many other circuits facilitating communication like modems, atomic clocks, radio telescopes, operation of telephone trunk lines, cable tv setup boxes, and much more.


2. Which is an Active Device in an LC Transistor Oscillator?

  1. Biasing Circuit

  2. Transistor

  3. LC Tank Circuit

  4. None of the above

The answer to the question would be option B: Transistor.

Explanation- In an LC transistor circuit, the transistor taps DC inputs (voltages) received are transmitted to AC outputs (waves). An inductor and capacitor body is used for boosting sustained oscillations, generally used in tunes, RF modulators, sine wave generators with the transistor playing an active role in the oscillation procedure. Varied oscillations process in a similar pattern, with the transistor aiding along with continuous and undamped of desired frequencies as long as the tank circuit is efficiently connected.