Hello, TI does not typically characterize the SAR based converters for under sampling; at these lower input frequencies most customers prefer to use the high speed pipeline converters. The input bandwidth is largely determined by the input sampling capacitor and sample switch resistance, and is useful for determining worst case noise bandwidth of the input signal. High performance devices like the ADS8881 use an internal error correction algorithm to determine the lower LSB's of the result. At higher input frequencies, this algorithm breaks down and the AC performance will decrease quite a bit, long before the 3db input BW is reached. For that reason, we do not recommend most higher performance, 16b or greater, SAR adc's for under sampling. You could use the ADS8881 , but the performance will be similar to a 12-14b ADC in these conditions. Most of TI's mid performance (12b, 14b, and some 16b) SAR ADC's use the more common SAR structure and can be used for under sampling. We do not have an exhaustive list of devices, but a few that are known to work are the ADS7042 and ADS7854 . As far as specific performance specs such as SFDR, you would need to measure that in your target system as we do not have any characterization data under these conditions. Regards, Keith N. Precision ADC Applications
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