# How does negative feedback increase bandwidth

## How negative feedback increases bandwidth

You have to realize what Bandwidth actually means.

The bandwidth is the frequency at which the gain decreases with increasing frequency. So if the gain decreases (with feedback) emotional At this point (where the gain starts to drop) to a higher frequency, then the bandwidth is increased.

Let's take an example of an amplifier. It has a frequency response as shown below: This amplifier has a voltage gain of 1 million but a bandwidth of only 10 Hz.

This plotted gain of this amplifier is the maximum it can achieve. There can never be more reinforcement than this. It is easy to see from the diagram that the maximum gain depends on the frequency of the signal. At 1 Hz the gain can be 1 million, at 10 kHz the gain must not exceed 1000.

We can use feedback to reduce , the gain, make the gain less than the value of the plot. This also shifts the point where the gain drops to the right. This is because the gain curve continues to apply. If, through feedback, we decrease the gain to 100 and then above 100 kHz, the gain will still decrease because the gain cannot be above 100 kHz 100 (blue dotted line).

Since the gain x bandwidth remains constant and we have reduced the gain by a factor of 1 million / 100 = 10 thousand, we can expect the bandwidth to increase by a factor of 10 thousand, so the 10 Hz time 10 thousand = 100 kHz. Here the blue dotted line crosses the "Open Loop Gain" curve.

The resulting transfer curve of the amplifier with feedback would then look like the green curve on the diagram below. In the illustration under the blue curve, the gain is shown in the open control loop. Please do not compare the numbers in both representations, I only took them from the Internet, they do not apply to the same amplifier. That is crucial shape of the curve and the relationship to the gain curve in the open loop. 