Paralleling AD8429 for lower input noise

I have build a 1000x LNA using AD8429 (data sheet schematics for DAC-coupling) and I'm quite happy with the result.

However, I would like to lower the input referred noise (1 nV sqrtHz) even further by paralleling multiple AD8429 (4x) to reach 0.5 nV sqrtHz noise levels.

Feasible? Should I use separate gain-setting resistors for each?

Thanks!

  • 0
    •  Analog Employees 
    on Dec 9, 2020 7:29 AM

    Hi nicolai.sidenius@icloud.com,

    I haven't actually tried paralleling multiple amplifiers to reduce the noise, though, we have a great article about the advantage of paralleling amplifiers to increase SNR performance here: (https://www.analog.com/en/technical-articles/paralleling-amplifiers-improves-signal-to-noise-performance.html ) The article described in detail the SNR calculation of multiple amplifiers in parallel and how the input referred voltage noise density is reduced. I would think this is feasible though there will be increase in current noise doing this scheme. Is this the increase in performance you're trying to achieve?

    With regards to the gain-setting resistor, it's advisable to use a separate for each AD8429 as you want it to be as close as possible to the device since it's stated in the datasheet (page 16) that parasitic capacitance at the gain setting pins may affect the CMRR of the device over frequency.

    Let me know if you have more questions nicolai.
    Though I may have missed this, but where's the schematic for DAC-coupling again? I didn't seem to see it within the AD8429 datasheet.
    Thanks.

    Another article for paralleling multiple amplifiers this is with regards to output drive: https://www.analog.com/en/technical-articles/paralleling-amplifiers-increases-output-drive.html 

    Best Regards,
    Dann