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Topic: Hi frequency noise on op-amp (Read 595 times) previous topic - next topic

Bergie

I've build a small op-amp circuit that is being driven by the stock standard "tone follower" sketch in the examples. No problem there. As expected it outputs a square wave. (Arduino Uno)

I've noticed a very high frequency on the positive pulses with my oscilloscope. I got about 33Mhz 2mV perfect sine superimposed on the trace. Even straight from the board I get this noise. My scope's grounded properly and I use GND on the Arduino as my scope ground as well. I'm sure this is the clock frequency of the UNO.

What is a quick and safe way of blocking the stray signal from my output? Even the blinky LED have this signal superimposed on the pulses. Its no serious matter right now as I'm mostly fooling around, but it did give me some problems driving my op amp. (For some reason, that signal goes in one side and out the other, although I think that is more to do with my breadboard layout than anything else.)
Thank you

Senso

The uno runs at about 16Mhz and not 33 or 32, but it can be a second harmonic from the crystal.

Bergie

Mmmm, now that I think about it, it may be 16Mhz... :~ I may have very well measured only half a cycle, thus the 33Mhz, quite common with me. Will re-check tomorrow if I get some time. Thanks

Grumpy_Mike

Quote
more to do with my breadboard layout than anything else

There is your answer, if you are using breadboard then the layout is going to be rubbish and you are going to get some feedback (positive) that will cause the oscillations.
Small capacitors (about 47pF) from the + and - inputs to signal ground will probably kill it.

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