Difference Between Positive Feedback and Negative Feedback

Feedback is the result of the process that has the potential to either trigger the process for more or inhibit the process to decline. The feedback from the output signal, therefore, feeds back to the input signal.

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In other words, the feedback process is when the actions of some event or system are fed back to the source of that event.

Feedback is a biological occurrence where the output of the system amplifies or inhibits the system to maintain the homeostasis to keep the internal environment in organisms constant.

Positive Feedback vs Negative Feedback

The difference between positive feedback and negative feedback is that in positive feedback the signal at the input source is the summation of the original fed signal and the feedback signal from the output that in turn increases the input signal while in negative feedback, the signal at source is the difference of the original signal and feedback signal that tends to make input signal weaker.

Positive feedback vs Negative feedback

A feedback loop can also occur on a larger scale in an ecosystem where a form of homeostasis is maintained. Without this feedback, the ability to self-regulate in organisms is lost.

Feedback systems are widely used to make circuits of the amplifier, process control systems and various other types of systems. To use feedback effectively, it should be controlled as uncontrolled.


 

Comparison Table

Parameter of ComparisonPositive FeedbackNegative Feedback
The relation between Input and Output signalInput signal and output signal are in the same phase.Input and output signals are in opposite phases with respect to each other.
Effect on the input signalMakes the input signal stronger.Weakens the input signal
Final outputFinal output is greater than the gain of the signal.Smaller than the gain of the system.
StabilityDecreases the stability of the system.Increases the stability of the state.
UsesMostly used in oscillators.Used in electronic amplifiers.

 

What is Positive Feedback?

Positive feedback or Regenerative feedback is when the fed signal and the output signal add up to give a stronger source signal. During positive feedback in the system, both the input and the output signals are in the same phase.

Positive feedback has the tendency to increase the overall gains of the system. It works by taking the output from the system and feeding it back to the source.

A positive feedback loop occurs in biological processes when the product obtained from the reaction becomes a catalyst for further reaction. In homeostasis, positive feedback takes the system away from the state of equilibrium.

The positive feedback is mainly used to make the circuit of various oscillators such as the RC Oscillator, Wein-bridge Oscillator, etc. Other uses of positive feedback are power stabilization, voltage and current control, current mirrors, signal sharpers, etc.

Wherever there is a need to regulate signal strength, positive feedback is used.

positive feedback
 

What is Negative Feedback?

Negative feedback occurs when the input and the output signals are in opposite phases or are at 180° with respect to each other. Negative feedback is also named as degenerative feedback.

The two signals in the negative feedback get subtracted and their difference derives the system. The negative feedback decreases the overall gain of the system because the output is subtracted from the source.

A negative feedback loop occurs when the product of the reaction leads to the slowdown of the reaction. This process brings the system closer to equilibrium.

Negative feedback is responsible for the stabilization of the system since it reduces the overall gains.

One of the most important role of negative feedback is in electronic amplifiers. Negative feedback is used in operating bandwidths, reducing distortion and noises caused by the external factors in the system and making linear operations possible.

negative feedback

Main Differences Between Positive Feedback and Negative Feedback

  1. When the input signal and output signal are in the same phase, they add up to give the stronger source signal, the process is positive feedback whereas, in negative feedback, the signals are out of phase with respect to each other.
  2. In positive feedback, the overall gains of the system are increased while in negative feedback gains of the system decreases.
  3.  In positive feedback, output received increases the rate of process and in negative feedback, output tends to decrease the rate of process.
  4. Positive feedback takes the system away from the state of stability while negative feedback increases the stability of the system.
  5. Positive feedback is mostly used in oscillator circuits while negative feedback is used in electronic amplifier circuits.

References

  1. https://www.medicine.mcgill.ca/physio/mackeylab/courses_mackey/pdf_files/ferrell_2002.pdf
  2. https://science.sciencemag.org/content/321/5885/126.abstract
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