Hi,
I have been experiencing the following issue with the sigma delta ADC ADS131A04. My input to the ADC is an 8Hz sine wave (from a signal generator) through a 3rd Order Butterworth LPF with a cutoff frequency of 500Hz and then into channel 1 of the ADC.
At 1khz sampling the 8hz sine wave seems to have the greatest attenuation then when sampling at the higher frequencies as shown in snapshot below where:
BLUE = 8hz sine wave sampling at 1khz
CYAN = 8hz sine wave sampling at 2khz
MAGENTA = 8hz sine wave sampling at 4khz
GREEN = 8hz sine wave sampling at 8khz
I have been suspecting that this attenuation is coming from the sinc3 filter of the ADC due to its magnitude response however at this 8Hz frequency, the change in the attenuation at 1/2/4/8khz from the sinc3 filter (in the order of magnitude of 0.999980260) is very very small when compared to the change that is being experienced in the sine wave digitized plots below
Could there be any other source from the ADC that is resulting in this attenuation whilst changing the sampling frequency?
Thanks
Johann
