The filter requirement is lot less complicated when compared to an anti-alias filter since the out-of-band attenuation of 20dB will be good enough to nearly eliminate Modulator saturation by out-of-band signals. We can implement a
Feedforward Low-pass filter to easily get 20dB kind of out-of-band attenuation and without adding any noise sources in the signal band. Therefore there is no noise
spec for this filter and hence it will be less power hungry.