After detailed analysis of the influence of non-ideal factors (such as device mismatches, voltage dependency of carrier mobility and temperature-varying effect) upon the performance of the double-MOSFET block including non-linearities cancelling, a circuit model for the double-MOSFET block via device physics approach is proposed. The effects of some non-ideal factors upon the performance of the block are analysed and simulated, based upon the proposed model, which is justified by SPICE-2 simulations.