Question

What is the total harmonic distortion if the amplitude of first harmonic distortion is 20dB, second harmonic distortion 25dB and external noise is 10dB?

(a) 11.2dB

(b) 11.52dB

(c) 11.25dB

(d) 11.5dB

The question was posed to me in my homework.

This interesting question is from Higher-Order Harmonic Distortion topic in portion Large Signal Amplifiers of Electronic Devices & Circuits

Answer 1

Right option is (c) 11.25dB

The explanation is: The total harmonic distortion is calculated by the formula given below. Given the first harmonic distortion V1 = 20dB, V2 = 25dB and N = 10dB:

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

THD + N = 1.25 + 10 = 11.25dB.