关于仪表放大器的问题！

电路画得看着别扭啊. 低通滤波器

我又重置了一张图，电路连接应该没有错误。如图所示。

问题：OUTA和REF 与 A4运放的连接关系我不是很理解其作用？这样的目的是什么？

截图可能看不太清http://www.deyisupport.com/cfs-file.ashx/__key/communityserver-discussions-components-files/52/2364._EA4E68883E652759216ADF62E8900652_.pdf

这是PDF的.

这个就是Sallen-Key拓扑结构的有源低通滤波器。

图中 C30起什么作用呢？ 这里有些不明白

想要搞明白C30的作用得先了解Sallen-Keyf拓扑结构，你可以看下这本书：

http://www.vyssotski.ch/BasicsOfInstrumentation/AnalysisOfTheSallen-KeyArchitecture.pdf

里面有提到基本的工作原理是：

The operation can be described qualitatively:

• At low frequencies, where C1 and C2 appear as open circuits, the signal is simply buffered to the output.

• At high frequencies, where C1 and C2 appear as short circuits, the signal is shunted to ground at the amplifier’s input, the amplifier amplifies this input to its output, and the signal does not appear at Vo.

• Near the cut-off frequency, where the impedance of C1 and C2 is on the same order as R1 and R2, positive feedback through C2 provides Q enhancement of the signal.

谢谢你的解答，我在认真的看下 ！ 非常感谢！