How to design 3rd order RC filter

[xiexi]

I want 4kHz LPF, I design R=780K, C=10pF, and 3 same RC in series, the -3dB is about 4KHz, is the design right?
if right but the size is too big to integrate in IC, can anyone give me some instruction to design a low cost LPF, thanks!

 

[gevy]

You can use active RC filter.
For example, see FilterLab Filter Design Software
**broken link removed**
for help.

 

[caosl]

Generally you can calculate the transfer function in mathcad or in matlab, then decide you filter's type(butterworth or some else), in matlab, these filter's transfer function have been given, so convenient to define the value of elements!