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[SOLVED] microvolt signal amplifier

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Paul98

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Hello, i need to create a circuit can gain a very small signal input like some microvolt with a bandwith from 0 to 500Mhz. The input device consist a coil with a max 100ohm of impedance. The inpedance depend how much winding have the coil but more round would be more sensivity in the input signal (it actually depends on how many feet of copper wire I use :D ). For example the AD620 OpAmp i think he have enougth sensivity but do not work in high frequencies. The output gain need to be some volt (or less if if enougth) in order to use (for example) a J-Fet like second stage. If necessary I could also evaluate a balanced output to possibly reduce background noise if the IC produces a lot of it (i hope no). I can design and simulate the circuit by myself (I hope. I already did).
So the question is: What components should I use to amplify this type of signal? Suggest name please

Thanks for the help
 

KlausST

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Hi,

Really 0 Hz? It should amplify DC? up to 500MHz?
from microvolts on? With a gain in the millions?

I doubt such a thing exists. I never needed them.

At first I´d verify the requirements.
Then I´d look for "current feedback OPAMPs"

Klaus
 

FvM

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Start with a simple consideration. 1 nV/sqrt(Hz) over 500 MHz gives 22 uVrms noise. That's the noise of a 50 ohms resistor, your amplifier has most likely higher noise. In so far "some microvolt" doesn't make sense.

Presume a cryogenic amplifier operated at liquid helium temperature is not in your scope.
 

Paul98

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Thanks for the info! . OK I exaggerated in requests. 0Hz was to say. The AD620 allows to detect some Hz though. Then let's do this. If I wanted to keep all the other parameters which component can I use which has the maximum bandwidth starting from a few Hz and which allows me to drive a further next stage? Therefore;
1) Frequency: 1Hz - Maximum available
2) Input: Minimum possible voltage close to microvolt - Output that allows you to manage a subsequent amp stage.
My main problem is an IC that is sensitive to these micro voltages. The rest is perhaps simpler, don't you think?
 

d123

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Hi,

Browse op amp parametric search tables on manufacturer's websites, look for op amps that handle inputs down to 0V and that have input offset voltages lower than the signal you want to capture, be aware that a bandwidth of 1 MHz usually means 10 kHz max. in reality.

Also, look for application notes about how to understand op amp datasheets and parameters.

Have a look at the difference between voltge feedback amplifiers and current feedback amplifiers.

You have a lot of reading to do, I'm afraid, give yourself maybe a week to research op amps and get an understanding of them for your needs, good luck.
 

danadakk

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Some info on cascaded stages -


Keep in mind as your G stage runs out of G at higher freq it loses its ability to reject CM
signals. Pile on that noise, PSRR, non linearities (you have not stated accuracy constraints)
you have a challenging problem on your hands.

There are receiver circuits in radios that take uV signals and G them up, but accuracy not
a characteristic, and its done in a narrow BW around freq of interest.

Some broadband RF MMICs -

https://www.rf-microwave.com/en/motorola/mwa230/hybrid-amplifier-to-39/mwa230/?filter=q1YyMrdQsopWMlCK1QGyLUFsMwMoUIqtBQA=



Regards, Dana.
 

Paul98

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Hi!

thank you so much for all suggestions and link!. @danadakk the RF MMIC you mentioned seem to be a good point to start. @d123 thanks for all links . I give a read!.
I would like to ask two questions and who can answer:
What is the value that describes the input sensitivity of a gain device? I believe this is the parameter that in the datasheets describes the ability to handle very low signals. I have seen that there are also some Jfet if they could handle small signals. In particular, the Jfet OpAmp which, being tendentially newer, could have better characteristics in this sense.
 

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Noise parameters (noise voltage and current density) are most important for the ability to handle small signals, in combination with gain, input impedance and bandwidth.
 

danadakk

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What are you doing with the signal after amplification ?

Regards, Dana.
 

Paul98

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I have a friend who is a radio amateur intrigued me. Currently it is curiosity about the feasibility, could you think of using it for example as a pre gain on an RTL SDR? . Or in any case where there is a need to amplify signals that are naturally low. Another problem could be due to the design that if not taken care of in the mini details could (I think) create limits on the gain. It would therefore imply the use of waveguides for the signal at least up to the amplifier. For these reasons, you could use ready-made mocules like this on https://it.aliexpress.com/item/32910023861.html don't you think?
 

danadakk

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Cant seem to get the datasheet in english.....

Amatuer radio receivers these days < 1 uV sensitivity, approaching .1 uV.

There are a number of preamps already designed, kits, finished, by amateurs for radio
work.


Regards, Dana.
 
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