Negative feedback is a technique used in amplifiers to improve their performance and stability by feeding a portion of the output signal back to the input in a phase opposite to the input signal. This technique offers several advantages over positive feedback, which increases the effects of a change in output.

### Key Facts

- Stabilizes Amplifier Gain: Negative feedback stabilizes the gain of an amplifier by reducing its dependence on various parameters or variations in the supply voltage.
- Reduces Non-linear Distortion: Negative feedback helps reduce the level of non-linear distortion in large signal amplifiers.
- Increases Circuit Stability: Negative feedback helps stabilize the gain of an amplifier, reducing the impact of variations in temperature, frequency, or amplitude of the signal.
- Increases Input Impedance/Resistance: Negative feedback increases the input impedance or resistance of an amplifier.
- Decreases Output Impedance/Resistance: Negative feedback decreases the output impedance or resistance of an amplifier.
- Reduces Noise Level: Negative feedback cancels out the noises introduced by the amplifier circuit, resulting in a reduced noise level in the output signal.
- Improves Frequency Response & Bandwidth: Negative feedback, being a resistive network, provides a constant gain over a wide range of signal frequencies, improving the frequency response and bandwidth of the amplifier.
- More Linear Operations: Amplifiers with negative feedback exhibit a more linear relationship between the output and input signals, resulting in a more proportional response.

### Advantages of Negative Feedback

## Stabilizes Amplifier Gain

Negative feedback stabilizes the gain of an amplifier by reducing its dependence on transistor parameters or variations in the supply voltage, making the gain more consistent and reliable.

## Reduces Non-linear Distortion

Negative feedback reduces non-linear distortion, which occurs when the output signal is not proportional to the input signal. By canceling out non-linear components, negative feedback improves the linearity of the amplifier.

## Increases Circuit Stability

Negative feedback increases the stability of the amplifier circuit by reducing the impact of variations in temperature, frequency, or amplitude of the signal. This prevents the amplifier from oscillating or becoming unstable.

## Increases Input Impedance/Resistance

Negative feedback increases the input impedance or resistance of an amplifier, making it less susceptible to loading effects from the source.

## Decreases Output Impedance/Resistance

Negative feedback decreases the output impedance or resistance of an amplifier, making it more capable of driving loads.

## Reduces Noise Level

Negative feedback cancels out the noises introduced by the amplifier circuit, resulting in a reduced noise level in the output signal.

## Improves Frequency Response & Bandwidth

Negative feedback, being a resistive network, provides a constant gain over a wide range of signal frequencies, improving the frequency response and bandwidth of the amplifier.

## More Linear Operations

Amplifiers with negative feedback exhibit a more linear relationship between the output and input signals, resulting in a more proportional response.

### Conclusion

Negative feedback is a valuable technique in amplifier design, offering numerous advantages over positive feedback. By stabilizing the gain, reducing distortion, increasing stability, and improving input/output impedance, frequency response, and noise levels, negative feedback enhances the performance and reliability of amplifiers.

### References

- Need of Negative Feedback in Amplifiers
- Feedback (positive and negative feedback)
- Analog Circuits Day-11: Feedback Amplifiers

## FAQs

### How does negative feedback stabilize amplifier gain?

Negative feedback reduces the dependence of amplifier gain on transistor parameters and supply voltage variations, resulting in a more stable and consistent gain.

### How does negative feedback reduce non-linear distortion?

Negative feedback cancels out non-linear components in the amplifier circuit, improving the linearity of the output signal.

### How does negative feedback increase circuit stability?

Negative feedback reduces the impact of variations in temperature, frequency, or amplitude of the signal, preventing the amplifier from oscillating or becoming unstable.

### How does negative feedback affect input impedance?

Negative feedback increases the input impedance of an amplifier, making it less susceptible to loading effects from the source.

### How does negative feedback affect output impedance?

Negative feedback decreases the output impedance of an amplifier, making it more capable of driving loads.

### How does negative feedback reduce noise?

Negative feedback cancels out the noises introduced by the amplifier circuit, resulting in a reduced noise level in the output signal.

### How does negative feedback improve frequency response?

Negative feedback provides a constant gain over a wide range of signal frequencies, improving the frequency response of the amplifier.

### Why is negative feedback preferred over positive feedback?

Negative feedback offers several advantages over positive feedback, including stabilized gain, reduced distortion, increased stability, improved input/output impedance, better frequency response, and reduced noise.