Feedback circuit process, a part of the output is to feedback into the input. The fed-back signal may be in phase with or out of phase with the given input signal.
The principle of feedback is possibly as old as the invention of the first machine but it is only some 50 years ago that feedback has come into use in connection with electronic circuits. It has been very useful in reducing noise in amplifiers and making amplifier operation stable.
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Definition Of Feedback Circuit
Feedback is defined as the process in which a part of the output signal (voltage or current) is returned back to the input. The circuit by which the total job is done the circuit is known as the feedback circuit or the circuit by which the feedback process is done is called the feedback circuit.
Feedback process signals and as such are signal processors. The processing part of a feedback system might be electrical or electronic, ranging from very simple to highly complicated circuits. Simple analog feedback control circuits can be constructed using individual or discrete components, such as transistors, resistors, and capacitors, etc, or by using microprocessor-based and integrated circuits (IC’s) to form more complex digital feedback systems.
The amplifier which operates on the principle of feedback is called a feedback amplifier.
An amplifier is a device that amplifies the signal is given to it. In an ideal amplifier, there are some important characteristics like voltage gain, input impedance, output impedance, bandwidth, etc. These parameters of an amplifier are controlled by applying a feedback network. Thus, a feedback network is appointed in an amplifier so as to control the gain and other factors of the device.
A feedback amplifier generally consists of two parts. They are the amplifier and the feedback circuit.
Types Of Feedback
The process of injecting a part of the output energy of some device back to the input is known as Feedback. It has been proved that feedback is very useful in reducing noise and making the amplifier operation stable.
Depending upon whether the feedback signal increase (aids)or decreases (opposes)the input signal, there are two types of feedback used.
- Positive feedback
- Negative feedback
It is a type of amplifier in which the input(or source) signal and the feedback signal are in the same phase. Hence, the feedback signal applied increases the strength of the input signal. or When the input signal and a part of the output signal are in phase then feedback is called Positive feedback. In other words, if the feedback signal (voltage or current) is applied in such a way that it is in phase with the input signal and thus increases the input signal then it is called positive feedback. It is also called regenerative or direct feedback.
- It increases the gain of the amplifier.
- If positive feedback is sufficiently large its leads to oscillation so it used in the oscillator.
- It increases the distortion and instability.
- Since positive feedback produces excessive distortion, it is rarely used in amplifiers. However, because it increases the power of the original signal, it is used in the oscillator circuit.
- Positive feedback always leads to instability. This characteristic of positive feedback is used in some applications such as active filters and oscillators.
- A normal application of positive feedback in digital electronics is forcing analog voltage values of a system far from their intermediate values into the digital state of 0 or 1.
In this type of amplifier input (or source) signal and the feedback, the signal is out of phase with each other. Thus, the feedback signal applied to decrease the strength of the input signal or When the input signal and part of the output signal are out of phase, the feedback is called negative feedback. In other words, The feedback in which the feedback energy i.e., either voltage or current is out of phase with the input and thus opposes it, is called negative feedback.
Though the gain of negative feedback amplifier is attenuated, there are many advantages of it such as,
- Stability of gain is improved.
- Reduction in distortion.
- Reduction in noise.
- Increase in input impedance.
- Decrease in output impedance.
- Increase in the range of uniform application.
- Bandwidth increases.
- Sensitivity will be decreased.
The main disadvantage of negative feedback decreases the overall gain. The gain and feedback factors in an amplifier are often functions of frequency, so the feedback may lead to positive feedback.
- They are used in almost all electronic amplifiers.
- They are used in regulated power supplies.
- They are used in amplifiers(amplifiers having a large bandwidth).