A single Op-Amp 0+2 sigma-delta modulator

This paper describes a single op-amp 0+2 ΣΔ architecture and design considerations to achieve 12-b resolution on a 2-MHz bandwidth. The proposed topology combines op-amp reduction and MASH techniques. In particular, the second-order ΣΔ stage uses direct synthesis of the noise transfer function (NTF) and employs only one op-amp. The use of multi-bit quantization on both stages increases the resolution of the modulator and reduces the output swing of the op-amp. The mismatch of the multi-level DACs can be compensated for with DEM while the mismatch between the two stages can be canceled in the digital domain. Simulation results, carried out at the transistor level with a 0.18-μm CMOS technology, verify the effectiveness of the proposed architecture. The simulated FoM is 104 fJ/conv-step.