We present in this work a systematic analysis to identify Sigma Delta Modulators (∑ΔMs) non-idealities, such as charge injection error, Input/Output conductance ratio error and settling time error. A physical mechanism behind Switched Current (SI) errors is proposed. In the first time, errors mentioned above are treated separately and a behavioural model of SI cell is derived for each non-ideality. In the second time, we propose a behavioural model of Non-inverting Lossless Integrator. For typical variations of SI-related errors, simulations have been made using Matlab/Simulink. Finally we present their influences on both dynamic and static performances of the 2nd order SI Low Pass ∑ΔMs (SI-LP∑ΔMs).