---
title: "Short note: Positive and negative feedback"
subject: "Basic Electronics Engineering"
chapter: 4
key: "semester_2/basic_electronics_engineering:short-note-feedback"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/short-note-feedback
site: BCT Engineering
---

# Short note: Positive and negative feedback

Basic Electronics Engineering · Chapter 4: The Operational Amplifier and Oscillator

- Asked in: 2072 Magh, 4 marks
- Video: [Types of Feedback Positive Negative - Feedback Amplifiers - Applied Electronics](https://www.youtube.com/watch?v=0nXEUkFBd8A) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/short-note-feedback
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-4

## Question

Write a short note on positive and negative feedbacks.

## Short answer

Positive feedback adds a portion of output in phase with input, increasing gain and enabling oscillation when Aβ=1; used in oscillators. Negative feedback subtracts, reducing gain but improving stability, bandwidth, and linearity; used in amplifiers. Both are defined by gain A and feedback fraction β.

## Answer

Feedback is the process of returning a portion of the output signal to the input of the amplifier. With gain A and feedback fraction β, there are two types.

```text
  Vs --> (+) --> [ A ] --+--> Vo
          ^              |
          +---- [ β ] <--+
```

#### Positive (regenerative) feedback

- The feedback signal is in phase with the input and adds to it.
- Gain: Af = A/(1 − Aβ). The gain increases.
- It reduces stability. If Aβ = 1, the circuit oscillates.
- Uses: oscillators (Wien bridge, square wave generator), Schmitt trigger, flip-flops and comparators with hysteresis.

#### Negative (degenerative) feedback

- The feedback signal is opposite in phase to the input and subtracts from it.
- Gain: Af = A/(1 + Aβ). If Aβ >> 1, Af ≈ 1/β, which depends only on the feedback network.
- Advantages: stable gain, reduced distortion and noise, increased bandwidth, better input and output impedances.
- Disadvantage: reduced gain.
- Uses: amplifiers, inverting and non-inverting op-amp circuits, voltage regulators.

| Point | Positive feedback | Negative feedback |
|---|---|---|
| Phase | In phase with input | Out of phase with input |
| Gain | Increases | Decreases |
| Stability | Poor | Good |
| Use | Oscillators | Amplifiers |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the gain with positive feedback?
   A. Af = A/(1 + Aβ)
   B. Af = A/(1 − Aβ)
   C. Af = 1/β always
   D. Af = A − β
   Answer: B. Feedback adds to the input, so gain increases. (Key point: Positive feedback gain)

2. Which is an advantage of negative feedback?
   A. Higher gain
   B. Oscillation without input
   C. Reduced bandwidth
   D. Stable gain, reduced distortion and noise, increased bandwidth
   Answer: D. Negative feedback trades gain for stability and bandwidth. (Key point: Negative feedback effects)

3. When Aβ >> 1 with negative feedback, what is Af?
   A. Af ≈ A
   B. Af ≈ 1/β
   C. Af ≈ Aβ
   D. Af ≈ 0
   Answer: B. Af = A/(1+Aβ) tends to 1/β, depending only on the feedback network. (Key point: Aβ >> 1)

4. Which uses positive feedback?
   A. Voltage regulators
   B. Inverting amplifiers
   C. Non-inverting amplifiers
   D. Oscillators and Schmitt trigger
   Answer: D. Positive feedback is used for oscillators, Schmitt triggers and flip-flops. (Key point: Uses)

## Related in Basic Electronics Engineering

- [Wien bridge oscillator circuit and operation](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Awien-bridge-draw-explain) — Basic Electronics Engineering, chapter 4, asked 4×

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