Question

What is the total harmonic distortion if the amplitude of first harmonic distortion is 20dB and second harmonic distortion 25dB?

(a) 1.2

(b) 1.52

(c) 1.25

(d) 1.5

This question was addressed to me in final exam.

Enquiry is from Second Harmonic Distortion topic in chapter Large Signal Amplifiers of Electronic Devices & Circuits

Answer 1

The correct answer is (c) 1.25

The best explanation: The total harmonic distortion is calculated by the formula given below. Given the first harmonic distortion V1 = 20dB and V2 = 25dB:

THD = (V2^2 + V3^2 +…+ Vn^2)^1/2 / V1 = (V2^2)^1/2 / V1 = V2 / V1 = 25 / 20 = 1.25