Colpitts oscillator operating at 50 MHz has an inductor in the feedback section of value 0.10µH. then the values of the capacitors in the feedback section is:
A)100 pf, 100 pf
B)100 pf, 50 pf
C)70 pf, 130 pf
D)80 pf, 60 pf

Question

Quizplus · Accepted Answer

The Colpitts oscillator's frequency of oscillation is given by $f = \frac{1}{2\pi\sqrt{LC}}$, where $L$ is the inductance and $C$ is the effective capacitance given by $C = \frac{C_1C_2}{C_1 + C_2}$ for capacitors $C_1$ and $C_2$ in the feedback section. For $L = 0.10\mu H$ and $f = 50 MHz$, solving for $C$ gives an effective capacitance. Given $C_1 = C_2 = 100pf$ results in the correct effective capacitance for a 50 MHz oscillation, assuming the formula and the parallel combination of capacitors are applied correctly.

Colpitts Oscillator Operating at 50 MHz Has an Inductor in the Feedback