Question

The operational amplifier uses differential input stage with a constant current source mainly to obtain:

• A. Very low common mode gain
• B. Very high differential gain
• C. Very low input noise
• D. Very high input resistance

Hint:

Differential input with constant current → suppress common mode and enhance differential gain.

Answer 1

The Correct Option is B

An operational amplifier (op-amp) often uses a differential input stage with a constant current source. Let's understand why this design choice is made:

Differential Input Stage: This part of the op-amp is responsible for amplifying the difference between two input signals while rejecting common signals. The precision and effectiveness of this process determine the performance of the op-amp.

Constant Current Source: By incorporating a constant current source, the op-amp ensures that the current through the differential pair remains constant, even as the input signals change. This stability in current helps achieve high precision in amplifying the differential input.

Given these characteristics, the main advantage sought through this configuration is:

• Very High Differential Gain: The combination of a differential input stage with a constant current source effectively suppresses the common-mode signals (signals common to both input lines) and allows the op-amp to achieve very high gain for differential signals. This design enhances the sensitivity of the op-amp to the differences between inputs while minimizing the influence of unwanted noise or interference that appears identically on both inputs.

Therefore, the correct answer is: Very high differential gain.