DC Unbalance Generation and Testing
With the rapidly increasing population of Power-over-Ethernet PSE’s (Power Sourcing Equipment), one of the most challenging measurements in the domain of Ethernet PHY testing is the relationship between link signal quality and DC current unbalance associated with large common-mode DC currents. This concern is heightened further by the availability of second generation PSE’s that source 30 watts of DC power on two pairs (one feed, one return). Small deviations from perfect signal balance have the effect of DC biasing magnetic secondary windings which in turn leads to magnetic core saturation. As transformer cores saturate, signal distortions from low frequency attenuation and reduced dynamic range create signal impairment and the potential of impaired link performance.
PVA-3102 test ports may be combined with Sifos PSA-3102 PoE test ports to produce automated analyses of PoE induced signal impairments via the mechanism of DC unbalance. Measurements include multi-pair SNR (non-linear distortion), low frequency PSD (Power Spectral Distortion), and estimated Droop (%). These measurements can be used to assess or qualify the Ethernet magnetics utilized in PSE ports.
DC Unbalance Test Configuration