Scaling Input Signal Swings of Overloaded Integrators in Resonator-based Sigma-Delta Modulators

Overloading of the integrators in loop filter of sigma-delta modulators is a performance degrading factor in circuit implementations. In this paper, it is shown that in resonator-based SigmaDelta modulators scaling factors should be introduced in order to adjust the integrators´ input. A systematic method is presented to calculate these scaling factors without modifying the noise and signal transfer functions. The effect of the scaling factors on circuit implementation is also discussed. Several examples are given to illustrate the influence of the scaling factors on the SigmaDelta performances depending on the order, architecture and number of bits of the quantizer.