In this tutorial paper we review Sigma Delta force feedback for the read-out of Micro-Electro-Mechanical (MEMS) inertial sensors with a discrete time loop filter. First we focus on the single feedback structure (with only mechanical feedback). It is shown that in this situation the mechanical transfer function introduces a zero in the overall loop gain. This gives rise to a constraint in the realizable NTF. In theory this can be overcome by adding a pole to the controller. An alternative solution is to add an extra electrical feedback branch. The latter solution is considered more beneficial in terms of power consumption and chip area.