Patent ID: 7532017
Filing Date: 2009-05-12
Classification: G01R,H04L

Abstract:
1. An AC maintain power signature detection circuit in a power sourcing equipment (PSE) for a Power over Ethernet system, the PSE providing a DC voltage to a power port of the PSE, the power port of the PSE comprising first and second power terminals to be coupled to supply the DC voltage to a load, the AC maintain power signature detection circuit comprising: a test signal generator circuit for generating an AC test signal at a first node, the AC test signal being a square wave at a first frequency and at a first set of voltage levels; a first diode coupled between a first power supply voltage and the first node; a sense resistor coupled between the first node and the first power terminal of the power port; a first resistor and a second resistor forming a first resistor divider for sensing a first voltage at the first node and providing a first scaled voltage at a common node between the first and second resistors, the first resistor divider having a first resistor ratio; a third resistor and a fourth resistor forming a second resistor divider for sensing a second voltage at the first power terminal of the power port and providing a second scaled voltage at a common node between the third and fourth resistors, the second resistor divider having a second resistor ratio different than the first resistor ratio, the second voltage and the second scaled voltage having a peak voltage being proportional to a load impedance of the load coupled to the power port and relative to the resistance of the sense resistor; and a comparator having a first input terminal coupled to receive the first scaled voltage and a second input terminal coupled to receive the second scaled voltage, the comparator generating an output signal having a first state when the first scaled voltage is greater than the second scaled voltage and a second state when the first scaled voltage is less than the second scaled voltage, wherein the AC test signal is driven onto the first power terminal of the power port through the sense resistor, the first and second voltages across the sense resistor are sensed by the first and second resistor dividers, the comparator compares the first and second scaled voltages and generates the output signal indicative of the load impedance at the power port.