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| 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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