Question

Which of the following FM demodulator is sometimes known as pulse averaging discriminator?

(a) Slope detection

(b) Zero crossing detection

(c) Quadrature detection

(d) Phase locked discriminator

This question was posed to me during an interview.

This intriguing question comes from Angle modulation topic in section Modulation Techniques for Mobile Radio of Wireless/Mobile

Answer 1

The correct answer is (b) Zero crossing detection

Easiest explanation: Zero crossing detector is sometimes known as pulse averaging discriminator. The rationale behind this technique is to use the output of the zero crossing detector to generate a pulse train with an average value that is proportional to frequency of the input signal.