In Fig. 26.16 can't we remove the φ₂ switches on the bottom of C₂ for

better operation? Won't keeping those switches create an error in the

output common-mode voltage?

The problem with removing those φ₂-controlled switches is that then there

isn't a DC path to V_CMFB. V_CMFB is only connected to capacitors or the gates

of MOSFETs (so its initial value is unknown and uncontrollable).

Yes, there will be an offset in the output common-mode voltage. This offset,

as discussed on page 875 is set by difference between the ideal V_CMFB and the

actual V_CMFB. In Fig. 26.16 the ideal V_CMFB is V_biasn.  

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