ADA4897 as ADC7124-4 Driver

Hi ADI,

I have a question regarding the maximum gain of ADA4897-2 and capacitive loads.

I use this amplifier with a gain =50 to amplifiy the sensor signal at the input of AD7124-4.

I use 100 ohm snubber resistor comes after a 2.2nF capacitor also another capacitor filter at the feedback loop.

Rg = 20 and Rf = 1k.

I want to know if this configeration makes op amp oscillates ?

I don't know how can I send the schematics if it can help.

Thank you in advance for your time and consideration.

6266.Schematics.zip



File: AD_Answer.docx
[edited by: mehdiaghayi at 12:09 PM (GMT 0) on 27 Jul 2020]

Top Replies

    •  Analog Employees 
    on Jul 29, 2020 5:48 AM 4 months ago

    Hi

    I would suggest to move or post this thread to the Amplifiers community as they may have better understanding about the product.

    I'm also curious, may I know what is your application and why do you need an Amplifier? Does the internal PGA does not meet this requirement?

    Thanks,

    Jellenie

  • Hi,

    Thank you so much for your information,

    In my application I must to distinguish a Voltage = 200µV (P-P) from the noise. So I need a noise figure below 20µV (p-p). Update rate also is another ristriction for which I can not use lower ADC noise below 13µV (p-P). This amplifier stage will add 3µV rms noise and is enough for me to achieve the 20dB SNR. Using the Internal PGA is good idea but, I have no information about the amount of noise that PGA will add to this stage. as you can see in the design I use a buffer amplier to reduce the  amount of resistors for Gain to reduce the noise.

    On the other hand, I designed for a Psuedoifferential ADC. It means that I produce a middle voltage 1.5 at AINM and also shift the measured voltage by 1.5. you can see it in the schematics. 

    Thank you in advance if you can tell me that can I do all the things above without amplifier? 

    Best Regards,

  • Hi,

    I moved the post to the amplifier community.

    To be clear, Can you propose me the method I can use to implement the mentioned circuit with PGA?

    Many thanks ,