two Questions about two step ADC architecture

[020170]

**broken link removed**

1. why SHA cannot connect with Fine Flash ADC directly?

in this figure, MSBs is coming from only coarse Flash ADC

but is it possible that every bits come from fine Flash ADC ?

2. why we use some A/D and D/A subtraction block?



thanks

 

[Davood Amerion]

This is like successive approximation register.
Coarse ADC produce output MSBs and it's difference with input voltage (SHA output) go to the fine ADC,
to produce fine bits LSBs.


Regards,
Davood.