Impact of high-order CoI filters on the output signal noise of incremental converters

• Published in: Microelectronics Vol. 84; pp. 115 - 121
• Main Authors: Soares, Antonio W.A., Catunda, Sebastian Y.C., Belfort, Diomadson R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2019
• Subjects: Analog-to-digital (A/D) converter; Cascade of integrator; Digital filter; Fourth-order modulators; Incremental sigma-delta; Input-referred noise; Sigma-delta (ΣΔ); Digital filter; Fourth-order modulators; Input-referred noise; Sigma-delta (ΣΔ); Incremental sigma-delta; Analog-to-digital (A/D) converter; Cascade of integrator
• ISSN: 1879-2391; 1879-2391
• DOI: 10.1016/j.mejo.2018.08.015

Incremental sigma-delta (IΣΔ) converters are adequate to be used in time-multiplexed multichannel measurement systems, where low frequency and high resolution are required. To achieve low latency channel switching, Cascade of Integrators (CoI) digital decimator filters are normally employed in these converters. Still, the search for higher resolution and bandwidth leads the designers to consider high-order converters, especially in multichannel systems. This paper presents a detailed analysis of the impact of using high-order CoI filters on the input referred noise of IΣΔ converters, which is affected by the different weighting of the filter coefficients. This analysis is carried out for a fourth-order Cascaded-Integrator/Feed-Forward (CIFF) modulator and a fourth-order CoI filter. Then, a general equation is derived that provides an approximation and upper limit of this impact for incremental converters of any order. Furthermore, the stability limits imposed by a single-bit quantizer in such converters is discussed. The proposed analysis is validated through several simulations performed at system-level using Simulink Matlab.