Topic: Analog Circuits
What is the output signal level of following circuit?
(The circuit is a non-inverting operational amplifier with $Z_1 = 10\text{ k}\Omega$ connected to ground, and feedback impedance $Z_2$ consisting of a $1\text{ }\mu\text{F}$ capacitor in parallel with a $40\text{ k}\Omega$ resistor. The input is a $1\text{ V}_{rms}$, $200\text{ kHz}$ sine wave connected to the non-inverting terminal.)
- A. ~5 $V_{rms}$
- B. ~1 $V_{rms}$
- C. ~4 $V_{rms}$
- D. ~0.1 $V_{rms}$
Answer: B. ~1 $V_{rms}$
Explanation: Voltage gain $(A_v) = 1 + \frac{Z_2}{Z_1}$
where, $Z_2 = (\frac{1}{j400\pi\times 10^3 \times 10^{-6}} \parallel 40\text{ k}\Omega)$
$Z_1 = 10\text{ k}\Omega$
So, $Z_2 = \frac{40\times 10^3}{1+j16000\pi}$
$|Z_2| \simeq 0.8\text{ }\Omega$
$\frac{Z_2}{Z_1} = 0.8 \times 10^{-4}$
$A_v = 1 + \frac{|Z_2|}{Z_1} = 1.00008$
$V_o \simeq 1\text{ V}_{rms}$.