1-Wire Bus PD Detection for PoDL Systems
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Solution Overview
Problem
Conventional Power over Data Line (PoDL) systems lack an effective low-current detection and classification scheme that can rapidly convey information before full DC voltage is coupled across the wire pair, limiting the ability to determine PD compatibility and parameters.
Innovation Solution
A half-duplex, serial 1-wire data bus is used for detection and classification, employing a low-magnitude pull-up current source and pull-down MOSFETs to communicate via a wire pair, allowing for the use of a novel low-frequency communication channel separate from the Ethernet PHYs, enabling the transmission of any desired information during the low-current handshaking phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional PoE detection and classification schemes are used, then the system can determine PD compatibility, but the communication is limited and slow due to requiring full DC voltage coupling
Solution Approach 1:
The patent performs detection and classification actions before full DC voltage coupling by using a 1-wire bus protocol during a handshaking phase. The PSE and PD exchange information through controlled voltage transitions on a single wire pair, allowing compatibility determination and parameter communication to occur in advance, thus reducing detection time and information loss.
2Productivity
If full DC voltage is coupled across the wire pair immediately, then power delivery is fast, but the system cannot determine PD compatibility or adjust voltage based on wire resistance
Solution Approach 1:
The system performs preliminary detection and classification by measuring wire pair resistance and determining PD compatibility through 1-wire bus communication before coupling full DC voltage. This preliminary phase allows the PSE to assess conditions and prepare appropriate voltage levels, ensuring both speed and reliability.
Solution Approach 2:
The patent changes the voltage parameter from full DC coupling to low-voltage 1-wire bus signaling during the detection phase. By using voltage transitions between defined thresholds (e.g., 0-0.5V for logic 0, 1.5-2.5V for logic 1) on a single wire, the system can communicate compatibility information and measurements without committing to full power delivery, thus ensuring reliability before productivity.
3Loss of information
If a 1-wire bus protocol is used for detection, then information communication is rapid and comprehensive, but the system requires a novel low-frequency communication channel separate from Ethernet PHYs
Solution Approach 1:
The patent makes the wire pair serve dual functions: high-speed Ethernet data transmission when fully powered, and low-speed 1-wire bus communication during the detection and classification phase. This multi-functionality allows the same physical medium to handle both information-rich handshaking and data transmission, reducing overall system complexity despite the added protocol layer.
Data Source
AI summary
A PoDL system includes a PSE supplying DC power and Ethernet data over a single twisted wire pair to a PD. Prior to coupling the DC voltage source to the wire pair, the PD needs to receive sufficient power to perform a detection and classification routine with the PSE to determine whether the PD is PoDL-compatible. The PSE has a low current, pull-up current source coupled to a first wire in the wire pair via a first inductor. This pull-up current charges a capacitor in the PD to a desired operating voltage, and the operating voltage is used to power a PD logic circuit. The PD logic circuit and a PSE logic circuit then control pull-down transistors to communicate detection and classification data via the first wire. After the handshaking phase, the PSE then applies the DC voltage source across the wire pair to power the PD for normal operation.