Cutoff frequency

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Image:Butterworth response.png In electronics, cutoff frequency (f_c) is the frequency either above which or below which the power output of a circuit, such as a line, amplifier, or filter, is reduced to 1/2 of the passband power; the half-power point. This is equivalent to a voltage (or amplitude) reduction to 70.7% of the passband, because voltage V² is proportional to power P. This happens to be close to −3 decibels, and the cutoff frequency is frequently referred to as the −3 dB point. Also called the knee frequency, due to a frequency response curve's physical appearance.

A bandpass circuit has two cutoff frequencies and their geometric mean is the center frequency.

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The term cutoff frequency can also mean the frequency below which a radio wave fails to penetrate a layer of the ionosphere at the incidence angle required for transmission between two specified points by reflection from the layer.

In physics, the term cutoff frequency will often refer to the plasma frequency, or can refer to some concepts related to renormalization in quantum field theory.

See also

• Low-pass filter
• High-pass filter
• Time constant
• Angular frequency

External links

• Calculation of the center frequency with geometric mean and comparison to the arithmetic mean solution
• Conversion of cutoff frequency f_c and time constant τde:Grenzfrequenz

es:Frecuencia de corte fr:Fréquence de coupure pt:Frequência de corte