多谢各位大侠，帮忙分析以下模拟电路的功能。

whwlxl

flushrat

Sallen-Key 2nd low-pass filter
H(s)=C1/(1+s/(W*Q)+s*s/(W*W))
W=1/sqrt(R1*C1*R2*C2)
Q=W/(1/(R1*C1)+1/(R2*C1)+(1-G)/(R2*C2))
G is the gain of opamp

flushrat

also you can calculate the transfer function by yourself, very easy.
To design this lpf, you must pay attention to W(bandwidth) Q(Q factor) and sensitivity(related to variation of R and C).
For example, the sensitivity of R1 to Q is:
S(R1,Q)=1/(1+R1/R2+R1*C1/(R2*C2)*(1-G))
if G=1, R1=R2, S(R1,Q)=0.5, it means R1's variation has little affect on Q
if G=2.9, R1=R2 C1=C2, S(R1,Q)=10,it means 10% variation of R1 will cause 10%*10=100% variation of Q.

whwlxl

很感谢， flushrat的回复。
因为我是学程序设计的，现在对模电很感兴趣，
自己看点以前学校的书，然后看看一些典型电路，
可是学的有些糊涂，特别是有些电路中电容的作用
到底是做啥的，完全不知道该怎么去分析。
希望能推荐本好书学习学习！

chenmingang

真牛

sunson

透彻，做模拟的就是要有这种细致，钻研的精神才行。

nanyu

牛牛牛

whwlxl

http://www.daycounter.com/Filters/SallenKeyLP/Sallen-Key-LP-Filter-Design-Equations.phtml

http://www.ecircuitcenter.com/Circuits/opsalkey1/opsalkey1.htm
很详细的电路说明，不错的模电网站！