LTC2323 Simulation in LTspice


I'm trying to simulate the ADC-LTC2323 16bit in LTspice in order to measure THD value of this converter and compare it with the datasheet. The model of the LTC2323 is available in LTspice. I'm connecting two sine signals to the differential inputs "ain-" and "ain+" of the ADC and then calculating THD with ".four " directive. The problem is that i'm getting too small THD values compared to those in the datasheet (ex: at fin=2MHz THD=4.5%=-26.9 dB, where according to the datasheet the THD should be -86.8dB at fin=2MHz). Is there something wrong with the model or my simulation isn't correct ??. Can anyone help??

Thanks in advance.