Is the output noise about 20mVpp normal?
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Please post your AMC1311 query in English - Thank you!
In Our AMC1311 test bench , Each output’ VOUTN ‘’VOUTP ‘ has about 20mppV noise.
II think this noise is too big compared to the datasheet values.
do you think it normal?
Output noise VIN = GND1, BW = 100 kHz 220 μVRMS
Hi Togasaki-san,
There is a chopper in the output stage of the AMC1311, where you can see some ripple around 625kHz when looking out VOUTp or VOUTn individually to ground. Differentially that noise should cancel. Could that be what you are seeing? Can you share an O'Scope screen shot?
Thank you for your answer.
The oscilloscope waveform will be ready.
You said that noise will be canceled. How is it canceled? I am observing "VOUTN" and "VOUTP" with a differential probe, but there is noise. best regards
Assuming the noise is equal amplitude and opposite phase on VOUTp and VOUTn, it will cancel in the end. Share your pics and we'll see if that is the case.
Hi Msatsugu,
the output of AMC1311 provides differential signalling. So, the common mode noise is eliminated by using a differential amplifier connected to the output of AMC1311 or by using an ADC with differential inputs. The common mode noise on both outputs is eliminated because both output signals are subtracted from each other. This is how differential signalling (also called balanced signalling) is working.
Also see this appnote:
Interfacing a Differential-Output (Isolated) Amp to a Single-Ended Input ADC (Rev. A)
Kai
thank you Kai
I would like you to look at the yellow waveform I sent you, and you will see that there is 20mVpp of noise on the output signal observed at the output with the differential probe. This means that there is normal mode noise on it. This is clearly caused by the AMC1311.
Hi Msatsugu,
I would like you to look at the yellow waveform I sent you, and you will see that there is 20mVpp of noise on the output signal observed at the output with the differential probe.
What is the green curve showing?
Due to the isolation barrier between input and ouput, the 480MHz carrier and the chooping frequency of 625kHz it can be difficult to perform an output noise voltage measurement. It depends on where exactly to connect the ground pin of scope and on how to handle the input and output grounds of AMC1311. It can be helpful to have a HF-path between the two input grounds during the measurement by the help of an Y-cap or so. Fullfill all safety requirements when connecting the Y-cap during the measurement, though.
Also, I would add a steep 100kHz low pass filter directly to the output of AMC1311. Without this low pass filter even with a differential probe the above mentioned HF-EMI may cause lots of aliasing artefacts destoring the measurement.
Kai