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Strange bump in spectrum

Question asked by AviAharoni on Feb 21, 2018
Latest reply on Feb 28, 2018 by musach

Hello,

We sample an Analog signal using AD7367 and then reconstruct it using AD5554. It is done almost simultaneously for 2 or 4 channels and we checked and there is no cross-talking between the channels.

We test 1 channel at teh time and the same problems appears in all of them: 

  When we sample at 41 Khz. we see a strange bump in the spectrum at 

15.5 KHz

When we sample at 65 KHz, this bump moves to around 19 KHz. See attached graphs for details.

We input the signal before the ADC and measure after the first amplifier on the DAC (see orange circle on schematics).

We got the same project with 1 channel using AD7457 ADC and AD5620 voltage DAC sampled at 90 KHz. and we don't see any bumps like that.

We also sample there without a filter immediately after the DAC

Could you please tell me what is the problem and how can we fix it?

We don't have such a sharp low-pass filter to remove this bump .

 

Regards,

Avi Aharoni

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