Passive, transformerless coupling circuitry for narrow-band power-line communications

The field of power-line communications (PLC) has been maturing and therefore much research is aimed at making PLC technology cheaper. In this paper we investigate passive coupling circuits as an alternative to transformer-capacitor couplers, as the coupling transformer is a relatively expensive component. Various other sub-fields of PLC such as modulation and coding have received a lot of attention in recent years, whereas the sub-fields of coupling, filtering, impedance adaptation and protection have lagged behind. Most electronic circuits, especially filter circuits have been around for years and perhaps their design is sometimes viewed as exhausted. However, the nature of the power-line grid requires careful consideration, as sensitive modems are to be connected to the power-line network, via these coupling circuits. These couplers further have to withstand the strain of relatively large voltages and currents. Hence, sufficient time spent, designing and selecting coupling circuitry elements is essential to avoid unnecessary attenuation as well as possible damage to the more expensive communication circuitry.