Class 12 > Unit # 22:Solid State of Electronics > Effects of Negative Feedback on Op-amp

Talha's Physics Academy

Negative Feedback and Effects on Op-Amp Gain

Negative Feedback in Operational Amplifiers

"Negative feedback occurs when a portion of the output signal, like voltage or current, is fed back into the input in a way that opposes or subtracts from the input signal."

Operation in Electronic Systems

Feedback is unidirectional, flowing from output to input, ensuring the loop gain remains independent of load and source impedances. A summing point at the input subtracts the feedback signal from the input signal, creating an error signal that drives the system.

Circuit Setup & Operation

The input voltage $V_{\text{in}}$ is connected to the non-inverting input ($+$) of an op-amp, while the output $V_{\text{out}}$ is fed back to the inverting input ($-$). With an infinite open-loop gain and no saturation, $V^+$ equals $V^-$. As $V_{\text{in}}$ changes, $V_{\text{out}}$ adjusts to maintain $V^- = V^+$.

Since $V_{\text{out}} = V^-$ and $V_{\text{in}} = V^+$, the closed-loop gain $G$ is given by:

$$G = \frac{G_o}{1 + G_o}$$

As the open-loop gain $G_o$ is very high (about $10^5$), there is little difference between $G_o$ and $(1 + G_o)$, making the closed-loop gain very nearly equal to $1$. This analysis holds true as long as the output voltage remains smaller than the supply voltage (e.g., between $-6\text{ V}$ and $+6\text{ V}$).

Fig: Circuit diagram illustrating an operational amplifier configured with negative feedback.