AD7400 : output waveform

Hello,

I have a question about the AD7400.

I connect the AD7400 with the FPGA.

The following waveform is the test input signal to the AD7400.

The signal is a sine wave of 100mV(1Hz) with the noise.

The following waveform is an output of the Sinc3 filter in the FPGA.

The noise of blue point doesn't appear in this waveform compared with the input signal.

Please let me know your advice about this cause.

Regards,

Mr.K