Signal Space Diversity (SSD) is one of the key technologies in the second generation of terrestrial digital video broadcasting standard (DVB-T2) where rotated constellation and Q-delay are employed to improve the performance over fading channels. In this paper, a novel projection-based design for the constellation de-mapper of DVB-T2 is proposed. The design uses several techniques to significantly save computations and energy without affecting the performance. Prototype results clearly indicate significant reduction of calculations as Eb/N0 increases with no performance degradation. The prototype design is 40% smaller compared to the latest published work with even better performance. The proposed design will be highly useful in low power DVB-T2 receivers. The idea and energy saving techniques can be easily applied to any rotated constellation de-mapper.