The input impedance of the following differential pair (for V_T = 25 mV and β = 100) will be:

Question

Question

This question was previously asked in

KVS TGT WET (Work Experience Teacher) 23 Dec 2018 Official Paper

Answer 1

Concept:

The input impedance of differential amplifiers is given by;

Z_i = 2βr_e

Where;

r_e = V_T/I_E

Calculation:

Given;

VT = 25 mV

β = 100

IE₁ = IE₂ = I_E = 5/2 = 2.5 mA

r_e1 = r_e2 = r_e = VT/IE = 25/2.5 = 10 Ω

Then;

Zi = 2βre = 2 × 100 × 10 = 2000 Ω = 2 KΩ