polyam wrote on May 6th, 2017, 8:11am:So, you would say there is no way to implement a passive adder for such a noise transfer function (1-z^-1)^2?
and the active one is the only solution?
No.
Surely understand passive summation.
How can you realze "K1=1.0, K2=2.5, K3=3.0" by R1, R2 and R3 ?
|K1|+|K2|+|K3|+|Kdac| > 1.0 is never possible.
Of course, you can not realize "K1=1.0, K2=2.5, K3=3.0, Kdac=-2.0".
K1=1.0, K2=2.5, K3=3.0, Kdac=-2.0
|K1|+|K2|+|K3|+|Kdac|=8.5
k1=K1/8.5=1.0/8.5
k2=K2/8.5=2.5/8.5
k3=K3/8.5=3.0/8.5
kdac=Kdac/8.5=-2.0/8.5
You have to compensate scale down of 1.0/8.5 by decreasing LSB of quantizer.
If your quantizer is a 1bit, compensation is not needed.