Adaptive maintain power signature scheme for power over ethernet system

Power over Ethernet (PoE) technology has been widely used in networking market for its space-saving, flexibility and low cost. As the PoE system needs to meet maintain power signature (MPS) requirements specified by the IEEE standard, it is important for powered device (PD) to draw a predetermined minimum current. If the PD current goes below the minimum current, the power sourcing equipment (PSE) assumes the PD has been disconnected and terminates operating voltage. If a fixed current is added to exceed the minimum current, a phenomenon of power wasting will be caused during standby or ultra-low power mode. This study proposes an adaptive MPS scheme to achieve power-saving and meet the MPS requirements. It consists of current comparator and MPS circuit to extract the periodic pulsed current for MPS requirements. The proposed scheme has been fabricated in 0.18 mu m 100 V Bipolar-CMOS-DMOS process adding no extra pin and an area is 1.45 x 2.23 mm(2). Test results show that the proposed interface sources a periodic pulsed current with a period of 318 ms and 25% duty cycle to tackle the issue of MPS absence in very low power condition.