I am conducting a study of the waveforms generated from human brain. I have to find out the presence of periodic signals in it and find out its frequency, amplitude (and amplitude shifts) and phase (phase shifts).
I don't really know anything about it. I am new to this field. I started a week ago. I have not read anything related to this subject (as you all can clearly see). For now, my task is to come up with a way to achieve lock-in amplification for a signal having a frequency of 100MHz. How to do that? I was kind of hoping that I could replace AD630 with another component and everything will be ok. But I think that is clearly not the case.
Who gave you this absurd task and told you it had anything at all do with "a study of the waveforms generated from human brain?" It doesn't.
Maybe you should review some of the research already performed in the study of human brain electrical activity.
Here is a link to a place to start. Nowhere is it ever mentioned that brainwaves occur at one hundred megahertz frequencies, nor is there any evidence of a physical biological mechanism that could generate or sustain such high radio frequencies.
All EEG or
electroencephalogram instruments operate at sub-audible, bandwidth-limited frequencies ranging from nearly direct current to about ten hertz, with only a few having bandwidths extending to about 100 Hz. Careful shielding of patient/subject and attaching leads, and minimization of patient/subject movement, is necessary to prevent myoelectric (muscle) currents from overwhelming the minute brainwave signals, which occur at nano-volt to micro-volt levels.
A lock-in amplifier
requires that a signal to be detected or recovered from noise be coherent with a reference frequency. This is not easily accomplished with brainwaves because
there is little to no one-to-one correlation between brainwave activity and an external stimulus. Exceptions do occur, for example if the optic nerves or the auditory nerves are directly monitored with implanted electrodes and external light or sound stimulus applied, but this is hardly sanctioned, non-invasive, EEG research, which I must assume is where your interests currently lie.