sheldon
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Eric,
Took a quick look at Gray & Meyer, rev. 4, and it seems like there is no perfect answer: 1) CMFB loops usually have more poles, so they need more compensation and therefore have less bandwidth. 2) CMFB don't supress common-mode noise unless they have gain at the frequency of the noise.
So the issue is that CMFB bandwidth is maybe good but difficult to achieve in practice, that is, it adds power/area/...
Sheldon
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