Why do the results for the ADCs and DACs graphs output from the BIST drop off more than the results of the ADC graphs in the data sheet?
The BIST does a sweep across frequencies, and so there will be a drop. The limits are essentially low to cover the range. The BIST could be better in that limits could be set per sample point, but there are no plans to change this. Also, we are using the DACs to sample the output from the ADCs so the quality is less for the given output rate when you have less samples at the higher frequencies. The characterization graphs of the ADCs that are in the data sheet, were performed using a signal generator and an oscilloscope.
The main difference when we characterize the cards is that the MATLAB ADC capture is used and the module is tested at coherent frequencies with appropriate inline filters used. It is the ADC capture data that is used in the actual data sheet.