Topic: Analog Circuits
A low pass filter as shown in following figure is built using an operational amplifier having unity gain bandwidth of 1 MHz. What is the bandwidth of this circuit?
(The circuit is a practical active low pass filter/integrator with $R_{in} = 100\text{ }\Omega$, $R_{f} = 10\text{ k}\Omega$ and $C = 160\text{ pF}$ in parallel.)
- A. 1 kHz
- B. 10 kHz
- C. 100 kHz
- D. 500 kHz
Answer: C. 100 kHz
Explanation: This is a practical integrator or active low pass filter. Its 3-dB bandwidth is determined by the feedback resistor and capacitor: $B.W. = \frac{1}{2\pi R_f C} = \frac{1}{2\pi \times 10\times 10^3 \times 160\times 10^{-12}} = \frac{1}{2\pi \times 1.6\times 10^{-6}} \approx 99.47\text{ kHz} \approx 100\text{ kHz}$.