A coherent receiver based on a 120° downconverter architecture, inherited from previous approaches at the microwave and optical fields, is proposed, analyzed, numerically evaluated and compared to the conventional 90° downconverter alternative. It is shown that, due to its superior calibration procedure, the new downconverter architecture allows full compensation of the imbalances in its optical front-end thus leading to an extended dynamic range and a broader operating bandwidth than its 90° counterpart. Simulation results from monolithically integrated downconverters show that our approach can be an interesting alternative to support efficient modulation schemes such as M-QAM that is being studied as potential candidate for the next generation of optical communication systems.