This article presents a self-powered interface circuit for the optimized synchronous electric charge extraction technique applied to piezoelectric vibration energy harvesting. A peak detector circuit is developed to detect the maximum and minimum vibration displacements and drive the electronic switches synchronously. This approach does not require additional piezoelectric elements to power the electronic interface itself for which a detailed analysis and a simple model are proposed to give a better understanding on the working principle. Finally, the influence of the switching phase lag and the peak detector power consumption on the harvested power is studied. Experimental studies are conducted and successfully compared with the theoretical approach.