What Is a Cutoff Frequency?

When the amplitude of the input signal is kept unchanged, the frequency is changed to reduce the output signal to 0.707 times the maximum value. That is to say, the frequency response characteristic is the cut-off frequency at the -3dB point. It is used to explain the frequency characteristic index. Special frequency.

When the amplitude of the input signal is kept unchanged, the frequency is changed to reduce the output signal to 0.707 times the maximum value. That is to say, the frequency response characteristic is the cut-off frequency at the -3dB point. It is used to explain the frequency characteristic index. Special frequency.

Chinese name

Cut-off frequency

Foreign name

cut-off frequency

Node value

-3dB

Cut- off frequency

: Use the modulus of the system function to represent the amplification of the circuit. Since 20lgA () =-3dB, the solution is A () = 10 ^ -0.15 = 0.7079457841 / 2, and because A () = | H (J) |, then | H (j) | ^ 2 = 1/2

There is a cut-off frequency at the high-frequency end and the low-frequency end, respectively called the upper cut-off frequency and the lower cut-off frequency. The frequency range between the two cutoff frequencies is called the passband.

Cut-off frequency photoelectric effect

When light hits the metal surface, electrons escape from the metal surface. But not all frequencies of incident light can cause photoelectric effect. For a certain metal material, only when the frequency of the incident light is greater than a certain frequency v0, the electrons can escape from the metal surface to form a photocurrent. This frequency v0 is called the cut-off frequency, also known as the red limit frequency, the limit frequency. The cutoff frequency is related to the cathode material, and v0 of different metal materials is generally different. If the frequency v of the incident light is less than the cut-off frequency v0, no matter how strong the light intensity of the incident light is, no photoelectric effect can be produced.

In simple terms, the cut-off frequency refers to the boundary frequency of a system's output signal energy that starts to drop sharply or rises sharply in a band-stop filter (usually at -3dB

Bandpass filter with cut-off frequency of upper limit f1 and lower limit f2

For the boundaries).

The relationship between cut-off frequency, open-loop cut-off frequency and closed-loop cut-off frequency

The open-loop cut-off frequency is also called the shear frequency. It is the frequency at which the amplitude-frequency characteristic curve crosses the 0dB line in the open-loop amplitude-frequency characteristic and is denoted as c. The closed-loop cut-off frequency is also referred to as the bandwidth frequency, which means that when the closed-loop amplitude-frequency characteristic decreases, When the frequency is 3dB below the decibel value when the frequency is zero, the corresponding frequency is recorded as b ^[1] .

The open-loop cutoff frequency is isotropic with the closed-loop cutoff frequency. The open-loop cutoff frequency and the closed-loop cutoff frequency are two different physical quantities that are used to describe the amplitude-frequency characteristics of the open-loop system and the closed-loop system, but there is a certain correlation between them, that is, the open-closed cutoff frequency and its unit. The closed-loop cutoff frequency of negative feedback increases in the same direction. And has the following relationship: b> c ^[1] .

Because the closed-loop cut-off frequency can be used to characterize the transient response speed of the closed-loop system, the higher the closed-loop cut-off frequency b, the faster its transient response speed. Since c and b are isotropic, the transient response speed of the system can be known from the Bode diagram of the system, that is, the higher the shear frequency c, the faster the transient response speed ^[1] .