Filter:
A filter is a filter circuit composed of capacitors, inductors and resistors. The filter can effectively filter out the frequency band or frequencies outside the frequency band of a specific frequency in the power line to obtain or remove the power signal of a specific frequency.
Filter is a kind of frequency selective device, which can let certain frequency components in the signal pass and greatly attenuate other frequency components. Using this frequency selection function of the filter, interference noise can be filtered or spectrum analysis can be carried out. In other words, any device or system that can pass a specific frequency component in a signal and greatly attenuate or suppress other frequency components is called a filter.