Participants : Marc, Yuhang
To test the effect of the amplifier we checked the spectrum of CH0 when disconnecting the amplifier :
FIg1 shows the CH0 spectrum when the voltage supply of the amplifier is disconnected but amplifier is still connected to CH2.
Fig2 shows the same with the ground also disconnected.
Fig3 shows the CH0 without the amplifier at all.
In all these configurations the peak around 20kHz is present : The 20kHz peak does not arise from the amplifier
We used the spectrum analyzer of the elec shop to check if the 20kHz peak is present in the voltage supply of this board.
Fig4 shows in yellow CH0 and blue the 1.8V supply : same peak in both at 17.4 kHz
Fig5 shows in yellow CH0 and blue before the regulator of the 1.8V supply : same as previous
Fig6 shows in yellow CH0 and blue the 24V supply : same as previous
Finally, we found out that the ground may be connected to all voltage supply of this board as well as DDS output channels (see connection.mp4)
Marc and Yuhang
We checked again the connection from ground to power supply or signal output today. And we realize that we were not checking in a good way last week.
This time, we measured the resistor between ground and many other parts. We found the resistor is as high as from 0.3kOhm to 0.9kOhm. In this case, it means the ground is well isolated with those channels. So there should not be ground issue.
For reference and future similar investigations :
The power supply was tested using a DC block (here up to 50V).
The ground was tested with the power supply disconnected.