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Measure 100microvolt signal?

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abicash

Member
Hello

I am in preliminary stages to design a circuit which measures minimum 100µv.

I have figured out that a 16 bit ADC will be sufficient for this (1 bit = 45microvolt for 3v ref)

Any tips,guidelines ,advice when measuring such voltages ?

Also which ADC will be good for such a thing?

Expecting help as usual ;)

Thanks & regards
 
Last edited:

ericgibbs

Well-Known Member
Most Helpful Member
Hello

I am in preliminary stages to design a circuit which measures minimum 100µv.

I have figured out that a 16 bit ADC will be sufficient for this (1 bit = 45microvolt for 3v ref)

Any tips,guidelines ,advice when measuring such voltages ?

Also which ADC will be good for such a thing?

Expecting help as usual ;)

Thanks & regards
hi,
Get the datasheet for the Maxim AD7705, dual 16bit adc, with inbuilt programmable gain amplifier.
 

abicash

Member
Hi guys

Thanks for replying :)

Well i haven't explained it quite correctly i guess.

Its actually a 20mv signal from a transducer which has to be brought at a 5v level so i will amplify it 250 times.
Now this 5 volt signal has to have a measurable voltage as low as 100µv.

So i was hoping 16 bit will be okay (just about!)

Oh and I will check the Maxim part...thanks

Thanks and regards
 

marcbarker

New Member
amplify first with an OP07, to lift your signal off the noise floor
EDIT: you're already doing that doh! sily me
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
100uV resolution on a 5V signal is a BIG project, layout and design will be absolutely critical - noise and layout problems can easily swamp the lower bits.
 

abicash

Member
Yes it is a big project :) and thats why i need some inputs.That was a good starting point Nigel but i really hope that you may post a link or something of this sort.If someone has already been through then it will be that much easier for me.Anyways comments like these are welcome :)
Thanks and regards
 

MikeMl

Well-Known Member
Most Helpful Member

Hero999

Banned
What frequency?

Use a digital automatic gain control.

You could use programmable gain amplifier and increase the gain if the signal level is too low.

This will give you a lower number of volts/bit at lower signal levels and a higher voltage/bit at higher signal levels.
 

ccurtis

Well-Known Member
You could use programmable gain amplifier and increase the gain if the signal level is too low.

This will give you a lower number of volts/bit at lower signal levels and a higher voltage/bit at higher signal levels.


That is a practical, cost effective, solution that I have seen in the real world. Often, only two gain levels are necessary and you can switch between the outputs of two cheap, fixed gain op amps with a cheap cmos analog switch. In that way, you can avoid compensating for output offset voltage changes, and other issues that come with changing the gain of a single amplifier in precision applications. Of course, in high speed applications that method is problematic due to the switching time and recovery time for the higher gain amplifier to come out of saturation.
 
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