Electronics > Projects, Designs, and Technical Stuff

High gain Transimpedance amplifier - 40 Hz noise

(1/2) > >>

arivalagan13:
I bought the OPA656 evaluation board and configured it as TIA with a gain of 10^9. Used application circuit from the opa656 datasheet.

I enclosed the amplifier in an aluminium shield to avoid EMI.

The amplifier is now connected to a CRO.

Now, I try to disturb the amplifier with body current (since I don't have a precision low current source), the amplifier is oscillating with a square wave with frequency roughly at 40 Hz. The amplitudes of the square wave are the saturating voltages of the opamp. The system is powered with +/-5V regulator which in turn powered from two 9V batteries and no transformers are involved in the design. The power supply is enclosed in a separate aluminium shield. Both aluminium shields are professional ingress protection box bought from SparkFun.



What could have gone wrong? The CRO is of analog type and with an only single trace. I checked the ground loop to my best and found to be ok with it. And by the way, for the information, the frequency at India is 50 Hz from grid power.

How do I troubleshoot such a problem?



Regards

M A

India

tggzzz:

--- Quote from: arivalagan13 on April 15, 2020, 04:40:21 pm ---What could have gone wrong?
How do I troubleshoot such a problem?

--- End quote ---

Many many things could have gone wrong.

You start by providing sufficient information for us to discount the unlikely possibilities. That should include a schematic, photos of the device's interior and exterior and test setup, and a photo of the output.

alanambrose:
Probably leakage or inadvertent coupling between output and input. A small parallel capacitor in the feedback loop (maybe only 1pF) will probably fix the problem.

Alan

arivalagan13:
I'll try to add one and update.

arivalagan13:
I'll update all the details.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod