A new digital current sensing technique suitable for low power energy harvesting systems

Solar energy harvesting captures the greatest attention among the available self-powered systems recently. This paper presents a new control technique based on digital current sensing. The idea is based on sensing the output current through a series resistance, the current sensor is a simple analog circuit, and it generates a pulse of width that is directly proportional to the rate of change of current. A pulse-to-digital converter is designed to convert the input pulse to a thermometer code. The code is then used to control a low supply digital controlled oscillator, it generates a clock that control the charge pump that searches for the maximum power of the solar cell. This design features a hill climbing maximum power search embedded inside the pulse-to-digital converter. A low dropout regulator with resistive ladder is used to control the supply of the oscillator, the oscillator supply is used as control knob for the frequency of the charge pump. The proposed control unit exhibits low power consumption, since it works at lower supplies than the energy buffer. The design can reach a power efficiency of 58.2% up to SmW available photovoltaic power. The measured power consumption is 36.33/iW. The system is designed using Global Foundries (GF 65nm).