Sigma-Delta ADC digital filter realizes 50Hz/60Hz interference suppression
In some high-precision Sigma-Delta ADCs of TI and ADI, both 50Hz and 60Hz power frequency suppression are achieved through digital filters. How is this suppression achieved?
In the sinc filter, if the decimation rate is W, then a notch will appear at (n/W)fs. If the first notch, that is, fs/W, is placed at 50Hz, the 50Hz power frequency will be There is a suppression of interference.
Similarly, placing the first notch at 60Hz will also suppress the 60Hz power frequency.
How to achieve simultaneous suppression? Just select different decimation rates at different stages of the sinc filter. For example, in the sinc3 filter, the first and second decimation rates select the first notch at 50Hz, and the third stage selects the first notch at 60Hz, then notch will appear at both frequencies, as shown in the figure below Show.
(In this picture, fs=125KHz, the decimation rate of the first stage and the second stage is 2528, and the decimation rate of the third stage is 2048. Of course, the order of the decimation rate can be adjusted at will)
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