filters: can someone explain the circuit?

[kasakachda]

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...

[just2rock]

Kasakachda,

See i dont worry of what the filters are or stuffs like that.What I look into the ckt. is that it uses the Op-amps to pass signal voltages ,from a specific I/p that you provide.Next it compares with the provided 5V supply accompanied with diff. Resistor values,as you can see to just modify it O/P's of the individual OPamps to rectify its Final O/p stage of the Recieving stage of RFID reader.
For more information on RFID, you can check my blog:--Go India

[sauravgoswami]

A communication filter circuit useful in a dual-mode receiver comprises a cascade of an active twin-T filter and a passive twin-T filter sections defining sharp notches at the center of second adjacent and of third adjacent channels, respectively, and specifically providing most attenuation at 60 kHz and at 90 kHz, for operation in the ISM136 band which has 30 kHz channel spacing. Since communication is channelized and limited in bandwidth, an active/passive twin-T notch filter structure is effective for signal attenuation. In a circuit in which real and imaginary signal components are processed, active-passive twin-T filters are provided in each of four signal paths, namely I and −I, Q and −Q. Buttersworth filter is used to filter out any noise or highpass filter and comparator is for voltage check!!,hope u got ur ans man

[adenco]

You could look into PIC 125 KHZ RFID SYSTEM DESIGN GUIDE