Question

For the circuit shown below, determine the Output voltage (Assume β=5, differential input resistance=12 kΩ)

(a) 4.33v

(b) 2.33v

(c) 3.33v

(d) 1.33v

I got this question during an interview.

The question is from Differential Amplifier and Circuit Configuration topic in chapter Operational Amplifier of Linear Integrated Circuits

Answer 1

Accurate option is (c) 3.33v

Here's an easy explanation: From the circuit dig, RC=10kΩ, Vin1= 1.3v and Vin2=0.5v,

 Differential input resistance = 2 βre,

⇒ 12kΩ = 2×5×Re

⇒ Re = 1.2 kΩ

Output voltage Vo = RC/2Re(Vin1-Vin2)

⇒ Vo =  10kΩ/(2 ×1.2kΩ) × (1.3v-0.5v)

⇒ Vo = 3.33v.