Design of high order single-stage sigma-delta modulator

Abstract

New arhitecture (named hybrid architecture for convenience) of sigma-delta modulator is proposed [ThKim98]. Hybrid architecture resolves the overloading and saturation problems by using the hybrid integrators. The dynamic range of internal nodes of modulator is guaranteed to have wide dynamic range that is enough not to degrade SNDR. Hybrid architecture is applied to the second order modulator and the fourth order modulator. In analog path, there is no global feedback, this reduces the redundant circuits to handle the feedback, and eliminates the chance of forming unwanted local loop. By use of overloading estimator, output value of each integrator doesn``t change twice in a cycle like overload detector of [Moussavi94]. In OLE, there are storing capacitors for each integrator, and OLE doesn``t need the additional clock phase. All integrator share the OLE to minimize the overhead. As for implementation, the digital loop is minimized to an integration block and some storage blocks, because the clock scheme operates no integrators simultaneously, and the modulator of proposed architecture is easily extended higher order. It can be shown clearly by comparing the second order sigma-delta modulator with the fourth order sigma-delta modulator. Consequently, The hybrid modulator provides the solution of overloading, saturation, and stability problem of high order modulator, and for large inputs. And circuit architecture gives a clock scheme for resource sharing, reduction of redundant circuit by eliminating the global analog loop feedback, and extensibility.