Why op amp is not used as an amplifier in the open loop configuration

Operational amplifiers (op-amps) are typically not used as amplifiers in open-loop configuration for several key reasons:

1. Lack of Precision and Stability:

   • Op-amps have inherent characteristics such as offset voltage, bias currents, and temperature drift that can introduce errors when operated in open-loop mode. These factors can lead to inaccuracies and instability in amplification.

2. Limited Gain and Bandwidth:

   • In open-loop configuration, the gain of an op-amp is typically very high (often in the range of 100,000 to 1,000,000). This high gain can lead to instability and oscillations in the output signal, especially at higher frequencies, due to the op-amp's limited bandwidth.

3. Saturation and Output Limitations:

   • Op-amps have limited output voltage swing and current drive capabilities in open-loop mode. They may not be able to provide sufficient output voltage swing or current to drive loads effectively without distortion or clipping.

4. Noise Sensitivity:

   • Open-loop op-amp configurations are more susceptible to noise pickup and interference, which can degrade the quality of the amplified signal.

5. Unpredictable Operation:

   • The behavior of an op-amp in open-loop configuration can be unpredictable and non-linear, especially near the supply rails or under varying load conditions. This makes it unreliable for consistent amplification without feedback.

Importance of Feedback:

• Stabilization: Feedback (closed-loop operation) stabilizes the op-amp by reducing gain and ensuring predictable and linear operation.
• Precision: Feedback reduces errors such as offset voltage and bias currents, improving accuracy in amplification.
• Control: Feedback allows the designer to control gain, bandwidth, and other parameters to suit specific application requirements.

Practical Use of Op-Amps:

• Inverting and Non-Inverting Amplifiers: These configurations use negative feedback to stabilize the op-amp and set a precise gain determined by external resistors.
• Differential Amplifiers: Used for amplifying the difference between two input voltages with high common-mode rejection, again utilizing feedback for stability.
• Summing Amplifiers: Combine multiple input signals with weighted contributions, benefiting from feedback to achieve accurate signal summation.
• Active Filters, Oscillators, and Comparators: These circuits rely on closed-loop feedback to maintain stability, precise frequency response, and reliable operation.

Conclusion:

While op-amps can theoretically amplify signals in open-loop configuration, they are not practical due to stability issues, lack of precision, limited bandwidth, and susceptibility to noise and other external factors. Feedback is essential in harnessing the full potential of op-amps, enabling stable, predictable, and precise signal amplification across a wide range of applications in electronics and communications.