Two issues that may need an improvement on the ADC hardware (V5, V6-0) were found: Use of 6.3V decoupling caps on +/-6.0V supplies, and low 1.8V supply to the ADC. The performance has been measured before and after proposed modifications to correct the ADC supply issues.
This work follows on from the previous reports which quantified all aspects of the performance of the ADC (see L1 alternative measurements).
Recommendations are to improve on V6-0 by the following changes:
Remove and short inductor L8
this improves the minimum supply to the ADC component and alleviates oscillations sometimes seen in the 1.8V power supply
the ENOB and SNR specifications stay the same with this modification
Change sixteen 6V3 rated capacitors used on +/-6V rails to 16V rated capacitors
this derating potentially improves the reliability of the cards
shows that ceramic capacitors may have much less capacitance than you think: a Y5V type may have only 10% of its rated value when it would have been used at its rated voltage. Also an X5R, when used at 30% of its rated voltage may have 10% less capacitance than you expect. And yes, we have seen an LDO oscillating because of this effect (see report).