Question

According to Millers compensation and pole splitting, what is the impedance in input port if I1 = 20 mA, I2 = 30 mA and Z = 2.3 kΩ?

(a) 0.38 kΩ

(b) 3.83 kΩ

(c) 0.57 kΩ

(d) 5.75 kΩ

I had been asked this question in a job interview.

This interesting question is from Miller Compensation and Pole Splitting in section Frequency Response of Electronic Devices & Circuits

Answer 1

Correct answer is (d) 5.75 kΩ

Explanation: To calculate the impedance in input port, given I1 = 20 mA, I2 = 30 mA and Z = 2.3 kΩ:

Zin1 = (1 + α) × Z

α = I2 / I1 = 1.5

Zin1 = (1 + α) × Z = (1 + 1.5) × 2.3 = 5.75 kΩ.