HDMI Active Cable PCA Negotiation Mechanism
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Solution Overview
Problem
HDMI cable assemblies face limitations in maximum cable length due to passive nature and increasing data throughput, leading to over-current protection issues when active cable assemblies draw higher currents from non-PCA capable source devices.
Innovation Solution
A method and apparatus for distinguishing between PCA capable and non-PCA capable source devices by asserting a reduced voltage on the power supply pin for a defined period, allowing increased current draw only when connected to a PCA capable source, preventing over-current protection fuse triggering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If active cable assemblies draw higher currents to extend cable length and enable active functionality, then cable length and functionality are improved, but over-current protection fuses are triggered in non-PCA capable source devices
Solution Approach 1:
The cable assembly performs preliminary detection of source device capabilities before drawing high current. The cable detects whether the source device is PCA capable through voltage detection on the power supply pin, and only then proceeds to draw the higher current required for active functionality and extended cable length.
Solution Approach 2:
The patent introduces an intermediary detection mechanism that mediates between the cable's power drawing needs and the source device's protection circuitry. By detecting source capabilities first, the system determines whether high current can be safely drawn, preventing fuse triggering while enabling active cable operation.
2Adaptability or versatility
If active cable assemblies draw higher currents for active functionality, then signal conditioning and repeating capabilities are improved, but current draw exceeds limits of non-PCA capable sources
Solution Approach 1:
The cable assembly dynamically adjusts its current draw based on detected source capabilities. When a PCA capable source is detected, the cable draws higher current to enable active functionality including signal conditioning and repeating. When non-PCA sources are detected, the cable limits current draw to legacy levels, adapting its operational mode to match source capabilities.
Solution Approach 2:
The system changes the operational parameters of the cable assembly based on source detection. The cable transitions between passive operation mode (lower current) and active operation mode (higher current) depending on whether PCA capability is detected, allowing signal conditioning capabilities to be enabled only when appropriate power availability is confirmed.
3Power
If voltage is asserted on power supply pin to enable PCA operation, then current draw capability is improved, but legacy devices may trigger over-current protection
Solution Approach 1:
The cable assembly uses feedback from voltage detection on the power supply pin to determine source capabilities. By monitoring the voltage assertion behavior, the cable can identify whether the source is PCA capable or a legacy device, and accordingly adjust its current draw to maintain compatibility while enabling advanced functionality when appropriate.
Data Source
AI summary
Methods and apparatus for the safe negotiation of high current for a High-Definition Multimedia Interface (HDMI) active cable assembly. In one embodiment, a method for detecting a Power for Cable Assembly (PCA)-capable source is disclosed, the method including: detecting, by a cable assembly, an assertion of a defined voltage on a power supply pin; forwarding an assertion of a hot plug detect signal pin, by the cable assembly, from a sink device towards the PCA-capable source; detecting, by the cable assembly, a reduction in the defined voltage on the power supply pin for a defined period of time in response to the forwarding; and detecting, by the cable assembly, a re-assertion of the defined voltage on the power supply pin subsequent to the lapse of the defined period of time. PCA dependent cable assemblies and PCA capable source devices are also disclosed.