External reference of AD9650

Hi miky 

Thanks for your interest in AD9650.

The "N/A" entry in Table 11 likely indicates that the exact voltage range for the external reference input is not explicitly defined in that table. However, based on the absolute maximum ratings, the external VREF pin can tolerate voltages from –0.3 V to AVDD + 0.2 V, which equates to 2.2 V when AVDD is 2.0 V.

Functionally, though, the ADC is designed to support reference voltages up to 1.35 V, which corresponds to a 2.7 Vpp full-scale input range. Therefore, the effective external reference input range is 0 V to 1.35 V, and the ADC input range scales as twice the VREF voltage.

Additionally, the use of an external reference may help improve the ADC’s gain accuracy and thermal stability.