Any app notes about how DC outputs are generated when noise is rectified inside OP-AMPs?
I believe you are looking for a way to calculate the resultant offset due to the internal noise of the amp. The app note at this link discusses a comprehensive way of calculating an error budget. A section in page 3 of the document touches on how to compute the error contributed by internal noise. The calculations are made for in-amps, but the same theory should apply.
You could also refer to this tutorial if you also want external components in your circuit included in the computations.
I will also refer you to this application note, which I realize may be quite old, but it extensively discusses noise sources and might provide a good foundation for your calculations.
I hope this helps. Let me know if you need anything else.
Thank you for replying
The problem is actually different
We have an external noise that gets into the opamp circuit and I believe it gets rectified internally by the junction diodes and gets amplified as DC voltage
Picture this, every time a “walkie-talkie” is turned on, the DC output level rises accordantly
I understand we need to filter any noise before it gets into the circuit, but I still would like to understand how this actually gets rectified inside the oapmp it self
Fausto Bartra, PEng
Tekran Instruments Corp.
330 Nantucket Boulevard
P: 416-449-3084 x 287
I believe what you're observing is the "detector" nature of your device with a circuit that is susceptible to RFI. Unfortunately there is no 'silver bullet' answer to this question because it is entirely dependent on the op-amp's own design and how it interacts with your design. Some devices are more immune or robust to RFI/EMI than others.
The simple explanation for the behavior, however, is that when you have a carrier of some energy at a particular frequency, a non-linear element (typically a diode) charges a capacitance which then introduces a lower frequency voltage based on the envelope of energy from the RF Interference. You can actually find out more about this phenomena under the subject of "Envelope Detectors" which are typically used for AM Demodulation.
I suspect, that in your case the RFI is in near-constant amplitude, but if you were able to subject the circuit to AM, you would likely be able to see the demodulation effect.
I hope this helps!
Retrieving data ...