Sorry about that. I'll try to explain it better.
Basically, the circuit has to be able to tell you if someone is breathing or not. That signal has a frequency of about 1Hz (since that is about the rate you breathe at). The problem is, the breathing signal has to be combined with another signal that can have a frequency from 10Hz to 10kHz. So my group were going to modulate the breathing signal by a 20kHz signal. This is so that the breathing signal and the 10Hz-10kHz signal can be combined and then later seperated with some RC filters.
The question was, is it possible to build our own modulator, or is there a cheap IC that can do this?
I hope this is not as confusing as my previous post.