# What is Threshold Frequency? Definition and Formula

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What is threshold frequency? Threshold frequency definition: In electronics, the threshold frequency is cutoff frequency, and it is the frequency of the output signal power when the output signal power of the circuit (eg, wire, amplifier, electronic filter) exceeds or drops below the conduction frequency. Or threshold frequency definition: Threshold Frequency is a characteristic frequency of a material, below which Photoelectric effect effect does not take place, no matter how intense the light is.

Frequency determines the Kinetic Energy of the ejected electrons, the intensity determines the rate of ejection of electrons. Alternatively, it is the minimum frequency required to eject an electron from the surface of a metal.

# What is Threshold Frequency? Definition and Formula

Normally, the output power is half of the conduction frequency at the cut-off frequency, and it is equivalent to the power represented by the position of 3 dB reduction on the Bode diagram, because the power ratio is at this point √(½)≈0.707. Output power to frequency band.

## Low-Pass Filter Cutoff Frequency

The following figure shows a first-order low-pass filter. Its cutoff frequency is determined by the following formula:

When the signal frequency is lower than this cut-off frequency, the signal can pass; when the signal frequency is higher than this cut-off frequency, the signal output will be greatly attenuated. This cutoff frequency is defined as the limit of the passband and stopband.

## High-Pass Filter Cutoff Frequency

The following figure shows a first-order high-pass filter. Its cutoff frequency is determined by the following formula:

When the signal frequency is higher than this cut-off frequency, the signal can pass; when the signal frequency is lower than this cut-off frequency, the signal output will be greatly attenuated. This cutoff frequency is defined as the limit of the passband and stopband.

## Bandpass Filter Cutoff Frequency And Passband Width

The right figure shows a Bode plot of a bandpass filter. As shown in the figure, f_l and f_r are the points where the low-frequency and high-frequency signal power is reduced by half, that is, the upper and lower cutoff frequencies.

The frequency range between the two cutoff frequencies is called “passband width”, and the frequency at the center of the passband is called f_0. Make “central frequency”.

Signals in the frequency range of the pass band can pass, and signals at frequencies on both sides of the cut-off frequency are greatly attenuated.

## Cut-Off Frequency and Passband Width of The Band-Stop Filter

Contrary to the band-pass filter, the band stop filter suppresses and attenuates signals in the vicinity of the specified frequency; signals in other frequency ranges pass smoothly. The right figure is a Bode plot of a bandstop filter.

Unlike the bandpass filter, which has two cutoff frequencies, the bandstop filter has only one cutoff frequency (at the intersection of the two concave lines in the figure)

### Threshold Frequency Conclusion

After going through the above portion of threshold frequency we can now establish threshold frequency definition. I hope you enjoy when reading this article, thank you.