In designing an active notch filter, which statement best describes how the notch center frequency is determined?

In designing an active notch filter, which statement best describes how the notch center frequency is determined?

• A. Center frequency is independent of the notch network values and is set by the supply.
• B. Center frequency is determined solely by the op-amp’s gain.
• C. Center frequency is determined by the notch network component values (R and C) in conjunction with the configuration.
• D. Center frequency cannot be tuned once built.

Answer: (C)

The notch center frequency is set by the notch network itself and how it’s wired into the amplifier’s feedback path. In an active notch, the RC values in the notch network establish the impedance versus frequency that the feedback loop “sees.” At a specific frequency, the network creates the conditions for maximum attenuation (a notch) when combined with the chosen circuit configuration, so the overall transfer has a zero (or very deep minimum) at that frequency. The op-amp then provides gain and buffering, shaping the overall response, but the actual center frequency comes from the RC values and how they’re connected in the feedback loop. That’s why adjusting the notch network components (R and C) or changing the configuration will shift the notch frequency. The supply voltage doesn’t set f0, and the op-amp gain mainly affects notch depth and quality, not the center frequency in the ideal case. And while you can tune the frequency by changing components, it isn’t inherently fixed forever once built.

The notch center frequency is set by the notch network itself and how it’s wired into the amplifier’s feedback path. In an active notch, the RC values in the notch network establish the impedance versus frequency that the feedback loop “sees.” At a specific frequency, the network creates the conditions for maximum attenuation (a notch) when combined with the chosen circuit configuration, so the overall transfer has a zero (or very deep minimum) at that frequency. The op-amp then provides gain and buffering, shaping the overall response, but the actual center frequency comes from the RC values and how they’re connected in the feedback loop.

That’s why adjusting the notch network components (R and C) or changing the configuration will shift the notch frequency. The supply voltage doesn’t set f0, and the op-amp gain mainly affects notch depth and quality, not the center frequency in the ideal case. And while you can tune the frequency by changing components, it isn’t inherently fixed forever once built.