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Embedded Files
Cutoff frequency
Cutoff frequency
A cutoff frequency/corner frequency/break frequency (fc) the point when a filter starts drastically reduces a signal's strength. It's the border of a system's frequency response at which energy flows through the system starts to reduce (attenuated or reflected) rather than going through.
[1] Often in electronic systems like filters and communication channels, it applies to edge in a lowpass, highpass, bandpass, or band-stop characteristic--a frequency characterizing a boundary between a passband and a stopband. It's at times taken as the point in the filter response where a transition band and passband meet.
E.g. As defined by a half-power point (a frequency the a circuit's output is ~−3.01 dB of the nominal passband value). Alternatively, a stopband corner frequency may be specified as a point where a transition band and a stopband meet: a frequency for which the attenuation is larger than the required stopband attenuation, which for may be 30 dB or 100 dB.
[1] In the case of a waveguide or antennas, cutoff frequencies correspond to the lower and upper cutoff wavelengths.
Electronics
Electronics
The cutoff frequency for an RC filter circuit formula is:
RC circuit
RC circuit
[1.1] a basic low-pass RC filter
Examples exercises
What's this circuit's cutoff frequency (fc)?
R = 400 Ω
C = 459 μF
fc = 1/2πRC = 1/(2π x 400Ω x 459μF) = 0.87 Hz
RL circuit
RL circuit
Examples exercises
What's this circuit's cutoff frequency (fc)?
R = 357 Ω
L = 345 mH
fc = R/2πL = 357Ω/(2π x 345mH) = 164.78 Hz
References
References
[1] Wikipedia
[1.1] Low-pass filter
[1.2] Frequency response
[1.3] Lowpass
[1.4] Highpass
[1.5] Bandpass
[1.6] Band-stop
[3] Low-pass Filters - All About Electronics
[3.1]
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