Non-linearities modelling and post-compensation in continuous-time Sigma-delta modulators

C. SCHMIDT; J. E. COUSSEAU; J. L. FIGUEROA; R. WICHMAN; S. WERNER

IET MICROWAVES ANTENNAS & PROPAGATION

INST ENGINEERING TECHNOLOGY-IET

Año: 2011 vol. 5 p. 1796 - 1804

1751-8725

The authors present a post-compensation technique for continuous-time (CT) SD modulators based on efficient finiteorder Volterra models. At first, the authors develop a behavioural model for a CT sigma?delta modulator (SDM). This model includes non-linear and non-ideal behaviour and leads to a finite Volterra representation of the SDM. Then, they derive and discuss two novel compensation blocks that are special cases of Volterra models. These models, a memory polynomial (MP) and a modified generalised memory polynomial (MGMP), can be interpreted as generalisations of classical block-based nonlinear models, like Hammerstein and Wiener systems, respectively. The authors show that the MGMP compensator offers a better distortion cancellation because of the inclusion of cross-terms at the output of the model, at the price of increasing complexity. Simulation results, based on a transistor level circuit model for the SDM, show a good agreement between the SDM and the developed models. In addition, the authors also verify good performance of the proposed compensators.