Can you help explain the following paragraph about anti-aliasing filter?

shijizai

Can you help explain the following paragraph about anti-aliasing filter? [Copy link]

Please help explain this sentence - "The 3db cutoff frequency of the anti-aliasing filter is 22KHz; when the sampling rate is 200ksps, it has 40db anti-aliasing suppression characteristics", looking forward to it~

Gen_X

If we analyze it according to the sampling law, the highest frequency is 22KHz. If we want to get a more complete analysis

The minimum sampling rate is 5-10 times the signal change frequency, which means the sampling rate should be above 110k.

Because it contains higher-order components that need to be identified or presented, the sampling should be around 220k to meet your needs at the minimum.

So let's round it up: the sampling rate is 200ksps.

This is called the sampling law.

shijizai

Gen_X published on 2021-7-8 16:07 If we analyze according to the sampling law, the highest frequency is 22KHz. If we want to get a more complete analysis, the minimum sampling number is 5-10 times the signal change frequency...

What do 3db and 40db mean?

Gen_X

That is to say, the degree of "pass". The definition of 1k high pass is: for 1k, a pass rate of 0.707 is passed. If it is lower than 1, the pass rate is close to 100%, and there is no attenuation. The attenuation here is the concept of db. I don’t remember whether 3db is 0.707, but this is basically the meaning.

Jack315

The anti-aliasing filter is a low-pass filter.

Used to reduce the aliased frequency components to a negligible level in the output level.

"The 3db cutoff frequency of the anti-aliasing filter is 22KHz; at a sampling rate of 200ksps, it has 40db anti-aliasing rejection characteristics"

This passage is probably a description of this low-pass filter indicator:

① Passband gain: unknown.

② Cut-off frequency: 22 KHz @ -3dB

③ Stopband attenuation: -40 dB @ 200 KHz