We are using AD9283 expansion module.. Setup: Feeding 3.3V 40MHz square wave; 180mV, 5 MHz single ended sine wave (at high Z) to the Ain+ SMA input, collecting the output samples into a PC and processing the samples in Matlab. Function generator, clock source and data collection system are all high end equipments. Input clock, 5.0V power supply, and the input analog signal are all clean. Observation: Sample values range from about 40 to about 250 (as seen from the Matlab time domain plot), a bit noisy.. When we compute SINAD using Matlab function, we get about 35 dB. However we expect about 47-48 dB of SINAD as per the data sheet of AD9283.. 13-14 dB is a huge degradation. Appreciate any suggestions/ thoughts.