need help on filters - pyroelectric detectors

[Natty]

hi

I need ur help. I want to know wat sort of filtering is done in the
first and in second stage!

I think in the first stage they have used high pass filtering and in
the second stage it is just amplification of the output from the first
op amp, the first stage.

Also, I wud like to know the reason for using a pull down resistor.

http://www.glolab.com/pirparts/appckt.pdf

I wud really appreciate ur help on this. thank you.

Natty.