I am using the AD7380 Eval board for evaluating the ADC performance.
It is having two differential input channels. INA and INB. I am giving input to channel B.
1) Sinusoidal input is taken from Function generator at 200kHz, 3.3Vpp then fed to Balun(MCL 3OH4 ADTT1-6 single end to differential end transformer) for single to differential conversion. Output of Balun (differential)is fed to channel B through twisted cable soldered at J3 and J4. SNR is showing less and also harmonics present. (Shown in figure 1)
2) One more thing is that even if I am not giving input from function generator(setup is connected as above ,only output of function generator was switched off), channel B FFT results in shifted noise floor(shown in figure 2).
I am unable to find the reason.
Kindly suggest. Thanks in advance.
The AD7380 evaluation board has an on board common mode voltage of 1.65V which derive from reference voltage , 3.3V(ADR4533) . The input signal of +/-1,65V(3.3Vpp) is offset by 1.65V common mode so that the voltage going into the AD7380 will be 0 to 3.3V. Please share how the connection of the BALUN and the AD7380 eval board was connected, I suspect this could be cause from the interaction of this voltage in the input. You mentioned that you try on channel B, Is it the same result when connected to channel A?
Thanks for your reply,
Our setup with balun is attached.
SMA connector is used for feeding signal to Balun.
This is being done only at channel B not at channel A.
Does the problem only occur on the channel B?? or same scenario with channel A? When the BALUN is removed, does the #2 scenario still exist? I can see that you run it using the 200kHz signal. Would you be able to run it at lower signal frequency like 10kHz. I often see a result like in #2, when there is over range in the input voltage. Would you be able to get a oscilloscope plots on the test points going into the ADC(AinB+ and Ain B-) and also if you can also get waveform plots snapshot in the software ( waveform tab of the AD738x software), this will give us an idea the waveform that the ADC is converting.
We have observed same issues in channel A also.
Would you be able to take a snapshot of the captured waveform in the AD738x software please. The snapshot would tell us the picture of the waveform entering the AD7380 that was captured. This waveform can be captured using the "Waveform" tab of the software. If you have some oscilloscope plots of the input signal it would be much better. Can you also check for me, if all the jumper connections are complete. (LK1, LK2,LK3, LK4, LK5).