Question

When frequency of oscillation of a crystal oscillator becomes parallel resonance frequency reactance of crystal oscillator becomes __________

(a) Zero

(b) Infinity

(c) Unpredictable

(d) Unity

I have been asked this question in class test.

This question is from Crystal Oscillator-1 topic in portion Oscillators of Analog Circuits

Answer 1

The correct answer is (b) Infinity

To explain: The oscillator has two resonant frequencies, parallel and series. Parallel resonance occurs when the reactance of series leg becomes equal to that of the parallel capacitor, and during this time, impedance offered is very high, almost infinite.