Basically, SDM has a high pass noise shaping in many case of the FNPLL design. You can design a SDM with effective bandwidth lower than the PLL loop bandwidth so that the SDM noise will be removed by the PLL loop.
In the case of PLL loop is fixed or can not change, you have to modify the order, quantizer level of SDM itself.
Here attached a simple paper from perrot[isscc97]
perrott_isscc97.pdf(1021.49 KB, 下载次数: 174 )