Currently I'm designing a pre-amp for detecting nanovolt-scale(~100nV, <1kHz) signal for experiment. I need a final gain to be around ~100000. Since the magnitude of the signal is extremely small, noise control is the major issue. So I am considering using AD8428 low-noise, fixed gain(G=2000) instrumentation amp (https://www.analog.com/en/products/ad8428.html) as the main amplifier and get some additional ~50 gain.

The two major options that I am considering to get the additional gain are,

  1. A subsequent AD8429 low noise variable gain in-amp
  2. PGA in ADC

And I have two questions.

  1. Is using in-amp(AD8429, https://www.analog.com/en/products/ad8429.html#product-overview) to get additional gain rather than using PGA is the better option in terms of noise-control? Or is there any other recommendation?

  2. If using additional in-amp is the best option, how should I stack them? It's hard to find a good method to stack two in-amps. Is there any good example?

I appreciate any advice you might have.

  • \$\begingroup\$ If you want proper help, please explain what/where your signal comes from because, it seems, that your error/noise budget is not well-founded. \$\endgroup\$
    – Andy aka
    Commented Jan 17, 2021 at 11:32
  • \$\begingroup\$ @Andyaka It’s hard to explain about the source since its one another big system under development, but the signal comes from electrodes detecting small change of electric field. The magnitude of the signal is expected to be pm 100nV by calculation (as stated above), and ambient EMI from radiation from normal indoor condition is also expected. The budget for the one channel will be around 100USD. :) \$\endgroup\$ Commented Jan 17, 2021 at 12:03
  • \$\begingroup\$ What is the bandwidth of the signal? DC to what frequency or... maybe it's got not DC content? Also what impedance is the source? \$\endgroup\$
    – Andy aka
    Commented Jan 17, 2021 at 12:15
  • \$\begingroup\$ @Andyaka Also as stated above, the band width should be about 1k. And the not sure about the impedance but lets say consider the electrode are on the air \$\endgroup\$ Commented Jan 17, 2021 at 12:31
  • \$\begingroup\$ But, does it contain useful DC components; it's important to state what the full spectrum of interest is in Hz or kHz. \$\endgroup\$
    – Andy aka
    Commented Jan 17, 2021 at 12:35


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