A Dual Band RF Energy Harvester System

Energy harvester circuit working as voltage source has wide application prospects in replacing the battery. How to obtain the energy efficiently in ambient environment has attracted more and more interests. Energy harvester can be used in Wireless Sensor Network(WSN) and it can both improve the service life and reduce the cost. Besides, energy harvester circuits can be also used in wearable device, which can increases the battery life and working life. Radio Frequency(RF) energy has the advantage of stability and wide distribution range and has been widely used in Radio Frequency Identification(RFID) chip. Collecting the RF energy in ambient is difficult compared to other type of energy harvester.This paper proposed a dual band RF energy harvester according to the frequency distribution character of the RF energy. The proposed harvester can collect 900 MHz band and 2.4GHz band RF energy simultaneously and can convert the RF energy into stable DC voltage to work as a voltage source. Compared to single band RF harvester, the proposed dual band harvester can improve the input power and increase the energy efficiency. The character of the traditional threshold-voltage self-compensation rectifier is instructed in detail. Based on the traditional structure, this paper reduces the threshold voltage by using the body effect. By combining the body effect and threshold-voltage self-compensation, the performance of the RF-DC(radio frequency to DC) converter has been improved significantly when the input power is low. The influence of the aspect ratio of transistor, the stage of the rectifier, the compensation order, and the gain of impedance matching network has been studied. And the rough output voltage of the RF rectifier has also been shown. According to the bandwidth of the two bands, the optimization of the parameter has been done for each band.To reduce the current consumption of harvester in charge mode, resistor-less bandgap reference and bias circuit is used. This not only decreases the power consumption but also reduces the chip area. A new type voltage detector is proposed for the harvester. The voltage detector uses a low power comparator to detect the voltage increasing and a high speed comparator to detect the voltage decreasing. By combing these technologies, the RF harvester just consumes 97 n A current in charge mode. To improve the integration level, DFC compensation LDO is used to guarantee the stability rather than using the ESR (equivalent series resistor). And the dominant pole is in the output of the first stage. Simulation results shows that the minimum input energy is-20 d Bm when the input frequency is at 900 MHz.