Electronics > Projects, Designs, and Technical Stuff
Oscilloscope 100x Pre-Amp for noise measurement?
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RogerThat:
Hi all,

I have a project with a 24-bit ADC reading an 0-50mV air pressure sensor. The thing needs noise free 5V power to be able to take fast measurement with the accuracy I want.

My oscilloscope (1054z) reads down to 500uV (actually less since there is noise)  and I need( maybe 'want' is a better word) to scope noise down to around 1uV. So, I'm thinking to build a 100x gain amplifier front end to the scope.

My basic idea is to use a 1ghz OP AMP with dual supply (two 3v lithium coin cells and two 2.048v references). This will give me a +- 2V output nicely match to the high gain mode on the 1054z. The thing needs to be battery powered due to noise...and yes, it's going in a metal can to shield off radio noise.

I've been playing with the idea since this morning so maybe the details are a bit off....but the idea. Have anyone done this before here? Maybe someone already have a schematic? 
HB9EVI:
Just some thought

My guess would be, that a 1GHz bw opamp doesn't necessarily have the best noise performance, and is quite obsolete, since you obviously work with a DC source.

In a setup with such an ADC, you probably have to care about mains frequencies, so 50/60Hz; some ADCs have filters builtin, additionally sample rate will be low to reach 24bits, what reduces noise of higher spectrum as well; so in the end we are mostly talking about 1/f noise
Kleinstein:
It is very difficult to get very low noise at a high BW. This is the reason for the usual 20 MHz filter setting with most modern scopes.

There is another thread about AC coupled amplifiers to measure low frequency nose.
In Vacuo Veritas:
Why are you yelling "op amp"? It's not an acronym. It's puzzling to me that so many people write "OP AMP". Why?
Conrad Hoffman:
The old Tek plug-ins go down to 10 uV/division. You'll be limiting the bandwidth to a few kHz max at that level if you expect to see much.
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