Estudio de la eficiencia de conversión RF-DC de un rectificador excitado por señales moduladas

Abstract

The RF-DC conversion efficiency of a rectifier when it is excited by digitally modulated signals is studied. This project is the first step to the implementation of a system able to transmit energy and information simultaneously. However, the study is focused on the energy transmission, therefore Wireless-Power Transmission (WPT). A rectifier, which is a device able to convert RF signals into DC is the key element in the system. In this project two rectifiers which work in the 900MHz band have been studied: the first one (dual-band) has a system called resistance compression network (RCN). This system helps the rectifier to keep the RF-DC conversion efficiency insensitive to changes in the load or in the input power. Also, this rectifier can work in the 2GHz band. The other rectifier (stub), has no RCN system. A variety of signals with the same average power but different complementary cumulative distribution function (CCDF), peak-to-average-power ratio (PAPR) and instantaneous power variance (IPV) properties are applied at the input of the rectifiers. In the transmission a root raised cosine filter is used. If the roll-off factor β is changed the RF-DC conversion efficiency will vary. It is shown if β presents high values, signals have low PAPR and IPV values, however, if β is near 0, the PAPR and IPV are high. Therefore, it can be seen that β can improve the RF-DC conversion efficiency. The effect of changing the average input power is analyzed. The main conclusion is the reduction of the optimum load value as the average input power increases The symbol rate has been studied. It is shown that the RF-DC conversion efficiency depends on the modulation rate through the output filter of the rectifier formed by the output capacitor and load value. It is shown that the IPV has the strongest effect into the RF-DC conversion efficiency. If the load resistor is high, signals with high IPV present a high efficiency, whereas, if the load is low signals with low IPV or continuous wave have better results than the previous ones. At last, it is seen that the diode has a big effect on the RF-DC conversion efficiency. When the output voltage reaches the diode breakdown voltage the efficiency drops. Comparing both rectifiers, the dual-band rectifier has worse peak efficiency than the stub rectifier. However, this rectifier can handle the variation of the load or the input power better than the stub rectifier.