I have purchased the EVAL-AD7682EDZ and EVAL-CED1Z and am building a receiver system. I have done some testing, using the PulSAR Software, on the EVAL-AD7682EDZ and EVAL-CED1Z setup and have stumbled across two problems:
1. When terminating the IN0 input I have noticed a voltage bias on the input using the PulSAR oscilloscope. My setup was:
ADC Internal REF = 2.5V,
ADC CFG Word = 3C01,
Oscilloscope y-axis setting = +-1.25V,
P5 jumper: pin 2 and 3,
P6 jumper: pin 2 and 3,
P7 jumper: not connected.
I would have assumed that the oscilloscope plot would show 0V. It is showing -1.15V on the plot. VBIAS on sheet 4 of the EVAL-AD7682EDZ schematic is measuring 1.26V and U13 output is 0.1V. Since there is an offset it is affecting the ADC dynamic range.
2. Using the same setup as above but imputing a known frequency; the PulSAR Spectrum is showing the output frequency at double the input frequency, i.e. fin = 10kHz and fout = 20kHz. It may be a setting that I have wrong but I just can't work it out. I have also plotted the output in MATLAB using the raw ADC data (which I saved to file using the PulSAR software) and I get the same problem.