The ADS117L11 uses a switched-capacitor, third-order, singe-loop modulator with a 5-bit internal quantizer. This modulator topology achieves excellent noise and linearity performance while consuming very low power. As with most high-order modulators driven by high amplitude out-of-band signals, modulator saturation can occur. When saturated, the in-band signal still converts, but the noise floor increases. Figure 8-7 illustrates the amplitude limit of out-of-band signals to avoid modulator saturation. The limit of dc and in-band signal amplitudes are 1 dB above standard full scale.

Modulator saturation is indicated by the MOD_FLAG bit of the STATUS register. The modulator saturation status is latched during the conversion period and is refreshed at completion of the next conversion. Modulator saturation resulting from out-of-band signals can be avoided by using an antialias filter at the ADC inputs. The Section 9.2 section describes an example of a fourth-order antialias filter; however, a low-order filter can be used with equal effect provided the amplitude is below the saturation limit.