Question

If C1 and C2 are the capacitance used in Colpitts oscillator the effective capacitance in the equation of frequency calculation is equal to ___________

(a) (ᴨ×C1×C2)/(C1+C2)

(b) 3 (C1×C2)/(C1+C2)

(c) (C1×C2)/(2ᴨ(C1+C2))

(d) (C1×C2)/(C1+C2)

This question was posed to me in final exam.

The query is from Colpitts Oscillator-2 in chapter Oscillators of Analog Circuits

Answer 1

Right option is (d) (C1×C2)/(C1+C2)

Easiest explanation: In the tank circuit of Colpitts oscillator there are two capacitors connected in series and hence effective capacitance is (C1×C2)/(C1+C2).