Question

What is the need for current source at emitter in differential amplifier?

Answer 1

I presume that you are asking about a typical opamp differential input stage made of two transistors with their emitters connected. The circuit has a differential mode gain and a common mode gain which is undesirable. Common mode gain decreases with higher impedance in the emitter circuit. A current source is far better than a voltage source with finite impedance for suppressing the common mode gain.

Answer 2

Answer:

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• I presume that you are asking about a typical opamp differential input stage made of two transistors with their emitters connected. The circuit has a differential mode gain and a common mode gain which is undesirable. Common mode gain decreases with higher impedance in the emitter circuit. A current source is far better than a voltage source with finite impedance for suppressing the common mode gain.