The search for compact autonomous devices has been increasing in the microelectronics industry. These devices have the capacity to generate their own energy in order to be charged. One of the ways of harvesting environmental energy for charging such devices is by using mechanical vibrations through the use of variable capacitor. Taking this principle a basis, this work presents a behavioral analysis of a system model of harvesting vibratory energy for low power, made up of a circuit which includes a variable capacitor and a piezoelectric transducer. An architecture of a circuit which improves the ratio “amount of harvested energy - circuit area” comparing with conventional architectures is presented. The conventional circuit harvested a maximum power of 4.5μW whereas the circuit with the new architecture harvested a 6.25 μW power. The paper shows a use of a piezoelectric generator providing initial power and compensating the leakage losses in the capacitors.