The filter chip I used is UAF42 from TI.
But if I add offset voltage to the circuit before the filter, the voltage going into the filter will become 0-5V. Can the filter able to filtering out the unwanted signals?
If the overall LP gain of filter is 0dB or 1 I see no problem, only offset problems may occur.
Added later:
Gain of UAF42 filter is 0dB. So you can change R14 to 12.5kΩ and connect pin 2 of R14 to +15V via 50kΩ resistor and filter output will have +2.5V offset. You may change R14 and additional resistor as appropriate.
the AC Signal is not blocked by the cap... only the DC component is blocked... If you need a large frequency range biasing circuit (from DC to AC) is better to use an OP amp, a voltage refference and 3 resistors to make your biasing circuit... if you need a schematic please drop me a PM,