A/D conversion at an early stage plays an important role for achieving such flexibility at the receiver. Analogto-Digital-Converter (ADC) constitutes a necessary component for the implementation of Software Defined- Radio (SDR) receiver. The goal of this paper is to present the behavioral models, implemented in the Matlab/Simulink environment. The SDR toolbox allows us to simulate at behavioral level most of the switched-capacitor (SC) sigma-delta (∑ ) Modulator non-idealities, such as sampling jitter, kT/C noise and operational amplifier limitations (finite bandwidth, finite DC gain, slew rate and saturation). Although very effective in simulating wide-band, medium-resolution !" converters the lack of a model for flicker noise and multi-bit quantizers makes this toolbox less attractive for simulating narrow band high resolution converters. The proposed extension not only fixes this limitation, but introduces a predictive model of the effect of capacitor mismatch in the internal multi-bit D/A converter.