Hi,
We have designed a board using ADS1278 and PGA280 for sampling 8 channels at up to 100 KSPS. With inputs shorted at ADC and at PGA, we have observed the following results (readings from the ADC):
1. With ADC inputs shorted: Noise (peak-to-peak) 96uV for Channel 1 and 149uV for Channel 8.
2. With PGA inputs shorted: Noise (peak-to-peak) 780uV for Channel 1
Between PGA and ADC, we have included the filter as suggested in PGA and ADC data sheets (50 Ohms resistors with 10 nF differential cap and 1 nF common mode caps). We are using 2.5V reference voltage (generated from REF5025). The PGA is working off +/-15V and +5V (VSOP,VSON).
The noise levels seem to be higher than expected. What could be the reasons for this?