In the context of active filters, the cutoff frequency and the -3dB frequency are related but not exactly the same.
The cutoff frequency, also known as the corner frequency or the 3dB frequency, is a point on the frequency response curve of a filter where the output power or amplitude is reduced by half (-3dB) compared to the maximum output power. It is the frequency at which the filter begins to attenuate the input signal. In other words, signals with frequencies below the cutoff frequency are passed through relatively unaffected, while signals with frequencies above the cutoff frequency are attenuated.
On the other hand, the -3dB frequency refers specifically to the frequency at which the output power or amplitude is reduced by 3 decibels (-3dB) compared to the maximum output power. The -3dB point is often used as a reference point for determining the bandwidth or effective range of a filter because it represents the point where the output power is half the maximum power.
In many cases, the cutoff frequency and the -3dB frequency are considered equivalent or used interchangeably because they are very close in value. In an ideal filter, the cutoff frequency and the -3dB frequency would be exactly the same. However, in practical active filters, there may be a slight deviation between the two due to various factors such as component tolerances, circuit design, and filter response characteristics.