Published:2011-7-14 0:57:00 Author:Joyce | Keyword: Power , Frequency , Noise , Filter | From:SeekIC
As shown in the figure is a power frequency noise filter circuit. This circuit shows a kind of double T filter, which can filter out noise of 50 Hz (or60 Hz) power frequency when magnifying (such as sensors etc) weak signals . If this sort of filters constitutes of RC components only, the value of Q is generally low, and it will have attenuation characteristics like that of the broadband. Using op-amp and add positive feedback can improve the value of Q. supposing that the value of Q is Q ', then Q '= Q / (1 - K), in which, K = RA / (RA RB). Changing coefficient K would increase the value of Q. The resonance frequency of the circuit fo is 1/2 πRC,and the positive feedback components are R / 2 and 2 C.
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