AD8676 popcorn noise

Hello,

I have some questions about the AD8675 (or 8676) and its popcorn noise.

I plan to use an AD8676 (or AD8675) in order to measure [0,1Hz;10Hz] noise of a low noise voltage source. I have chosen this amplifier as, according to the datasheet, it has great performances at low frequencies.

Here is a simple view of the circuit:

A capacitor and a resistor are used for AC coupling (fc ~0,8Hz). The opamp amplifies the signal with a 60dB gain. Then, another stage filters the output (not represented here).

In order to test my circuit, I short the input and look at the output. I then filter the output (fc=40Hz).  In theory, I should measure aproximately the amplifier (+resistors) noise times the gain.

You can find below some captures made with an osciloscope (voltages are in mV, 500ms/div).

We can see some noise alternating in between two levels (don't forget that the voltage has been amplified by 10000). This behaviour is strange and I tried to remove it by changing the resistors and the capacitors, none of it worked. Then I changed the opamp with another low noise reference (not an AD's one) and this noise disapeared !

This type of noise clearly is a problem for my circuit as it limits the noise levels I'll be able to measure.

So, I have a few questions for you :

- this noise looks like popcorn noise, is it correct ?

- do you have any data/information about this noise in your products ?

- do you have any advice to remove/reduce this type of noise

Thanks a lot for your time,

Have a nice day,

Jean-Baptiste



Added missing pictures
[edited by: JBjb at 3:12 PM (GMT -5) on 4 Jan 2021]
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    •  Analog Employees 
    •  Super User 
    on Apr 1, 2021 10:09 PM in reply to JBjb

    Hello Jean-Baptiste,

    So sorry that you did not get a resolution on the pop corn noise you've measured. I've been told that for the problem that you're seeing it's best that you reach out to your ADI representative and get them involved with Failure Analysis on the samples you're having issue.

    Again sorry for this not being pointed out to you earlier.

    Regards,

    Hooman

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