filters: can someone explain the circuit?

[kasakachda]

**broken link removed**

Hello there.
The circuit in the pic is used in receiving stage of an RFID reader. All I know is that the first two filters are active twin-t filters and the third one is a butterworth low pass filter.

Can someone confirm this. Also I need the design procedure for the same. Please help...

 

[crutschow]

Analysis of such circuits is not trivial. Doing it by hand is a real exercise in mathematical agility. The easiest way to determine the filters' characteristics is to simulate it with a SPICE program. Such programs are available for free from Linear Tech and TI.

Design of such active filters is easiest with a design program. Free programs from TI Active Filter Design Application - FILTERPRO - TI Software Folder or National Semi **broken link removed** generate the design for various filter types and configurations.

If you need any further info on active filter types just Google "Active Filters".

 

[kasakachda]

Can you please tell me how to find the cut-off frequency or bandwidth of each filter atleast?

 

[crutschow]

Can you please tell me how to find the cut-off frequency or bandwidth of each filter atleast?

This TI app note https://www.electro-tech-online.com/custompdfs/2008/05/sloa088.pdf lists the various active filter types. You find the equations appropriate to the filters you have and use the component values from your circuit to solve for the filter response. It requires a little bit of number crunching.