Need help in 4th-Order Source Follower Lowpass Filter design

[JondorZ]

Hi there,

I have a project to design a 4th-order source follower lowpass filter for medical applications. Here are the specifications:

   1. Supply Voltage: 2.5V
   2. Filter order: 4th-Order
   3. Cutoff Frequency: 3kHz, 5kHz, 8kHz, 10kHz programmable
   4. Power Consumption: <2mW
   5. Design Tech: 0.35um CMOS


I am using Cadence Virtuoso to design and simulate the circuit. I am designing the internal circuit of the opamp using NMOS and PMOS transistors. So I use the biquad design and it doesn't seem to be working. I need help in whether the biquad design is suitable or there is other better circuit design. Thanks a lot!

[audioguru]

I have always used Sallen and Key for lowpass and highpass filters.

[kbyrne]

From a newbi to this post there is a freeware and paid program called FilterWiz. It has what is mentioned here plus all opamp choices ect with necessary parameters.