SBASAH6A March 2022 – October 2022 ADS117L11
PRODUCTION DATA
Input signals occurring near fMOD (12.8 MHz in high-speed mode and 1.6 MHz in low-speed mode) fold back (or alias) to the pass band, resulting in data errors. When aliased, the frequency errors cannot be removed by post processing. An analog antialias filter at the ADC inputs removes the frequencies from the input signal before they are aliased by the ADC. The required order of the antialias filter is dependent on the selected OSR and the target value of signal attenuation at fMOD. A large value of OSR means more frequency range between the fDATA Nyquist frequency and fMOD for the filter to provide the desired roll off. For example, for OSR = 128, more than two decades of frequency separates fDATA and fMOD. With a corner frequency = fDATA, a third-order, 60-dB per decade filter provides a 120-dB alias rejection at fMOD.