Noise optimizing AD8599 &&

Good day,

I have a task to optimize noise in BW 10Hz - 10kHz.

Voltage gain shall be around 20..50. OA connected directly to source of signal,

which has impedance 1kOm DC and 50Om AC. OA connected to middle point of R1/R2 divider,

where R1 connected to OA (OUT), and R2 connected to GND.

1. For +5V supply we get not so many choice here - only OP284. (LM258 -noise not specified).

In AN-940 (attached) stated that it is optimized for 10kOm impedance,

which looks like too much for my case.

2. So, i have to use +5V&-5V supply. According AN-940, looks like best choise is somewhere between

AD797(450 Om  - single OA per case -) AD8599 (550 Om + 2 OA per case +)

ADA4004-2(1.5 kOm + 2 OA per case +)) & ADA4075-2 (2.5 kOm - + 2 OA per case +)

3. Currently, i get acceptable result with AD8599 & R1=12.5 kOm, R2 = 500 Om.

But, if it is optimal in my case? Shall OA chain be optimized as well?

4. AD8599 consume 5mA per OA. So, tempting to use ADA4075-2, as it consume less and

2-3 times cheeper as far it is not precise (offset 2mV).

Please share your thinking.

Thanks in advance!

BR

K

LowNoise_OA_selection_AN-940.pdf
  • Hi Adex,

    Thank you for considering ADI parts in you design. May I know what your application is?

    I would recommend ADA4528-2. It is a precision, ultralow noise, zero-drift operational amplifiers which features a patented chopping technique that suppresses offset-related ripple in a chopper amplifier. This chopping technique offers ultralow input offset voltage of 0.3 µV typical and input offset voltage drift of 0.002 µV/°C typical and is also suited for low frequency applications.

    The technique nulls the amplifier's initial offset in DC domain with a local feedback loop which prevents ripple at the overall output.

    You can also check out this link for more information on minimizing offset voltage and drift.

    Also, you may want to read this article on Zero-Drift Amplifiers.

    If you want a wider supply range, you could use ADA4522-2.

    I hope this helps.

    Regards,

    Roel


  • Hi rvieja,

    Thanks for taking part in discussion.

    Besides, chopping adds noise, isn't it?

    I am not interested in low offset and drift, to which

    chopping technics targeted to, I need optimize Noise:)

    BR

    K

  • Hi K,

    Yes you are right. Chopping adds noise. I reviewed our portfolio and you may want to consider ADA4898. It has a low input voltage noise of 0.9nV/sqrt(Hz) at 1kHz and has a source resistance of 375 Ohms.You may also want to check ADA4895 which has an input voltage noise of 1nV/sqrt(Hz) at 1kHz and has a Rs of 675 Ohms.

    I agree that we should optimize the noise of the op amp. But we need to know first some of the parameters of your input signal such as its signal range, noise and source impedance to be able to have a noise-optimized design. What's important here is that the noise coming from the amplifier should have a negligible effect to the overall noise of the system.

    If you could tell us more about what your application is, we could be able suggest to you a better part.

    Regards,

    Roel


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