CAPACITORLESS_NOTCH_FILTER

Published:2009/7/13 10:29:00 Author:May | From:SeekIC

The notch frequency for the filter is set by fnotch＋［（ALP/AHP）×(RZ2/RZ1)］×f0where ALP and AHP are the gain from input to low-pass output at f=0 Hz，and the gain from input to high-pass output at f≤f0，respectively． Typically （（ALP/AHP）×(RZ2/RZ1)＝1；therefore，fnotch=f0，and is gtven by f0＝1/(2π)(RFC)where RF＝RF1=RF2, and C＝C1＝C2. The －3-dB bandwidth is determined by the following relation∶BW－3dB＝fnotch/Q， where BW－3dB＝fH-fL. The Q of the filter affects the passband gainc(which should be adjusted to unity) and is related to the ratio of the resistances RZ3 to RZ1 and RZ3 to RZ2. In other words，Q＝(RZ3/RZ1)＝(RZ3/RZ2). Q also is related to RQ by the follOwing relation∶RQ＝(25 kΩ/Q-1).



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