应该是有源低通滤波器--
变形如下:<br />[img]https://bbs.21ic.com/upfiles/img/20091/200911935120963.jpg[/img]<br />[img]https://bbs.21ic.com/upfiles/img/20091/200911935236481.jpg[/img]<br />[img]https://bbs.21ic.com/upfiles/img/20091/200911935342620.jpg[/img]<br /><br />截止频率只能估计个大概,有时间最好自己仿真一下.
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