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Replacement for AD630 for the purpose of Lock-in Amplification

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John Manuel

Jun 7, 2018
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Hi,

I am trying to build a lock-in amplifier circuit using AD630. But the signal which I wanted to detect is in the megahertz range and AD630 is not functioning in this region. So, is there any device which can do lock-in like AD630 but in a higher frequency region?

Thank You.
 

hevans1944

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The usual approach is to use a mixer and a local oscillator to translate the information spectrum of the megahertz signal to a lower baseband frequency. But you haven't provided any information about the information spectrum of the megahertz signal. Please tell us WTF you are trying to do and let us decide whether a lock-in amplifier is appropriate to the task.
 

John Manuel

Jun 7, 2018
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The usual approach is to use a mixer and a local oscillator to translate the information spectrum of the megahertz signal to a lower baseband frequency. But you haven't provided any information about the information spectrum of the megahertz signal. Please tell us WTF you are trying to do and let us decide whether a lock-in amplifier is appropriate to the task.
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).
 

(*steve*)

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Wow, you're telling me that there are signals in my brain at frequencies around 100MHz?!?

What will you use as a signal that is synchronised with these signals? For lower frequencies I could see how you found stimulate the brain with a flashing light and use a lock in amplifier to extract synchronised electrical activity in the brain, but this is orders of magnitude faster.
 

Harald Kapp

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Are we dealing with the (unfortunatlely not so uncommon) wrong use of upper and lower case letters here?
M = Mega
m = milli
The latter being much more in line with the study of brain waves. Therefore 100 mHz, not 100 MHz. The AD630 should be able tho handle those signals.
 

John Manuel

Jun 7, 2018
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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.
 

(*steve*)

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The heart of a lock in amplifier is the 4 quadrant multiplier.

I would go to my favorite parts supplier and see what 4 quadrant multiplier they have. I know I've seen some that operate into the MHz range, but I've really not give looking for anything really fast.

And yeah... Check the frequency if it's really brainwaves your looking at.
 

(*steve*)

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Check out the AD834. Specs go to 500MHz
 

hevans1944

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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.
 

davenn

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and on that wonderful note

thread closed

The OP @John Manuel obviously has no idea what he is doing and needs to do some serious background reading before embarking on any brainwave recording projects

several links have been given and I would advise John to follow them
 
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