ZHCSIU4A September 2018 – August 2019 ADS1284
PRODUCTION DATA.
The low-noise modulator is an inherently-stable, fourth-order, ΔΣ, 2 + 2 pipelined structure, as Figure 38 shows. The modulator shifts the quantization noise to a higher frequency (out of the passband), where the noise is removed by the digital filter. The modulator data can either be completely filtered by the on-chip digital filter or partially filtered by use of the sinc filter section alone. Partial filtering provided by the sinc filter section is intended for use with an external FIR filter.
Modulator performance is optimized for input signal frequencies over the range dc to 2 kHz. As Figure 39 shows, the effect of PGA and modulator chop result in spectral artifacts occurring at the chop frequency (4 kHz) and harmonics related of the chop frequency. When using the sinc filter output in conjunction with an external post-decimation filter, design the external filter to suppress the modulator chopping artifacts.