Hi Tosei,

I think whether you implement a passive or an active adder depends on how much signal attenuation
you can accept. With reduced supply voltage, the signal swing in SD modulators has become smaller and
the attenuation of a passive adder cannot be tolerated anymore. Furthermore, the coefficients of a passive
adder are sensitive to parasitic capacitance. An active adder isn't and therefore often results in a more
roboust design.

Regards,

Thomas