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Electrical Engineering QUESTION #2186
Question 1
A Wien bridge oscillator uses $R = 10\,\text{k}\Omega$ and $C = 10\,\text{nF}$. The oscillation frequency and op-amp closed-loop gain required for sustained oscillation are:
  • $f_0 \approx 1.59\,\text{kHz}$, $A_v = 3$✔️
  • $f_0 \approx 1.59\,\text{kHz}$, $A_v = 2$
  • $f_0 \approx 15.9\,\text{kHz}$, $A_v = 3$
  • $f_0 \approx 159\,\text{Hz}$, $A_v = 1$
Correct Answer Explanation
$f_0 = \frac{1}{2\pi RC} = \frac{1}{2\pi\times10^4\times10^{-8}} \approx 1591\,\text{Hz} \approx 1.59\,\text{kHz}$. Barkhausen criterion for Wien bridge requires loop gain $= 1$; feedback factor $\beta = 1/3$ at $f_0$, so $A_v = 3$ (i.e., $R_f = 2R_1$).