In a Multiple-Feedback (MFB) active filter, what is the primary function of the feedback capacitors?

In a Multiple-Feedback (MFB) active filter, what is the primary function of the feedback capacitors?

• A. They set gain only.
• B. They determine Q and center frequency.
• C. They only provide DC blocking.
• D. They couple to ground.

Answer: (B)

In an MFB active filter, the feedback capacitors shape how the loop feeds back signals at different frequencies. Their reactances change with frequency, so the amount of feedback the op-amp experiences varies across the spectrum. This frequency-dependent feedback creates the second-order response, setting the natural (center) frequency and how tightly the circuit resonates, i.e., the Q factor. The center frequency is determined by the values of these capacitors together with the surrounding resistors, and the Q is set by the ratio of those values and the damping from the resistive network. So, the primary role of the feedback capacitors is to determine Q and center frequency. They do not primarily set DC gain, provide only DC blocking, or simply couple to ground.

In an MFB active filter, the feedback capacitors shape how the loop feeds back signals at different frequencies. Their reactances change with frequency, so the amount of feedback the op-amp experiences varies across the spectrum. This frequency-dependent feedback creates the second-order response, setting the natural (center) frequency and how tightly the circuit resonates, i.e., the Q factor. The center frequency is determined by the values of these capacitors together with the surrounding resistors, and the Q is set by the ratio of those values and the damping from the resistive network. So, the primary role of the feedback capacitors is to determine Q and center frequency. They do not primarily set DC gain, provide only DC blocking, or simply couple to ground.