Sigma-Delta force-feedback loops have to deal with a stability problem due to phase-lag occuring in the sensor. To tackle this problem traditionally a compensator is introduced in the loop. We show that this traditional approach imposes a constraint on the realizable NTF such that the NTF cannot be optimized.
Next we propose a novel unconstrained architecture that allows to implement any NTF. This way greatly improved quantisation noise shaping can be obtained. In a typical design example the improvement was 12 dB.