Question 10.3: a) Determine the frequency for the oscillator in Figure 10–2...
a) Determine the frequency for the oscillator in Figure 10–21 . Assume there is negligible loading on the feedback circuit and that its Q is greater than 10.
(b) Find the frequency if the oscillator is loaded to a point where the Q drops to 8.
(a) C_{\mathrm{T}}=\frac{C_1 C_2}{C_1+C_2}=\frac{(0.1 \mu \mathrm{F})(0.01 \mu \mathrm{F})}{0.11 \mu \mathrm{F}}=0.0091 \mu \mathrm{F}
f_r \cong \frac{1}{2 \pi \sqrt{L C_{\mathrm{T}}}}=\frac{1}{2 \pi \sqrt{(50 \mathrm{mH})(0.0091 \mu \mathrm{F})}}=7.46 \mathrm{kHz}
(b) f_r=\frac{1}{2 \pi \sqrt{L C_{\mathrm{T}}}} \sqrt{\frac{Q^2}{Q^2+1}}=(7.46 \mathrm{kHz})(0.9923)=7.40 \mathrm{kHz}
P R A C T I C E EXERCISE
What frequency does the oscillator in Figure 10–21 produce if it is loaded to a point where Q = 4?