Pre-amplifier of Flash A/D converter

[snola]

flash a/d

In the general way, the preamps of a flash a/d converter are differential outputs amplifier. If the output common mode voltage between two output terminal are different, then the common mode noise will become a huge problem. Hence, we will add a common-mode feedback circuit to adjust the common voltage for solving this problem. However, there are many types of preamp in flash a/d converter are not add common-mode feedbacks to solve common-mode noise. My question is there are not exist common-mode feedback circuits in the flash a/d conveter. Why?

 

[henry90176]

I think the preamps gain is small,so it doesn't require cmfb