This paper presents a compact energy harvesting system, which consists of an electromagnetic (EM) generator converting ambient low frequency vibrations to DC voltage by using a highly efficient full-wave rectifier in a System-on-Package (Sop). Frequency Up-Conversion technique has been utilized by the in-house EM transducer to harvest energy from very low frequency vibrations (<5 Hz). The interface ASIC is a passive rectifier based on the boot-strap rectification (BSR) technique to decrease the effective threshold voltage of the utilized diodes, attaining a high AC/DC conversion efficiency in a standard 0.35 mu m CMOS process. The energy harvesting system has been tested within a frequency range of 2-10 Hz. The autonomous system with a volume of 21 cm(3), delivers 128 mu W DC power to an 80 mu A load at an external vibration frequency of 2 Hz and 72 mg peak acceleration while a 1.6V DC voltage is generated. The maximum overall power density is measured as 6.1 mu W/cm(3). Furthermore, the reliable operation of a commercially available temperature sensor, as a realistic load, has also been demonstrated by using the energy harvester as a DC supply. (C) 2012 Elsevier B.V. All rights reserved.