A new algorithm for an incremental sigma-delta converter reconstruction filter

Image sensors dedicated for the applications of the Earth observation require medium-speed and high-resolution analog-to-digital converters (ADCs). For that purpose, an incremental sigma-delta analog-to-digital converter (IΣΔ ADC) has been designed. Post-layout simulations highlighted a degradation in resolution caused by the circuit imperfections. Therefore, a digital correction has been investigated. This paper proposes a new reconstruction filter which takes into account not only the bit values of the modulator output sequence but also the occurrence of certain patterns. This technique has been applied to an incremental sigma-delta analog-to-digital converter in order to correct the conversion errors. Performing with 400 clock periods for each conversion cycle, the theoretical resolution is 15.4 bits. Post-layout simulation shows that a 13.5-bit resolution is obtained by using the classical optimal filter whereas a 14.8-bit resolution is obtained with our reconstruction filter.