HDMI Protection Circuit Blocks DC Voltage
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Solution Overview
Problem
HDMI systems are vulnerable to abnormal short circuits caused by high DC voltage sources in automotive and aircraft applications, which can damage the high-speed serial lines using Transition Minimized Differential Signaling (TMDS) technique, as existing protection methods like ESD devices do not protect against permanent short circuits.
Innovation Solution
A protection circuit comprising a pair of electrical conductors, capacitors, and splitters that split the TMDS signal between an AC path and a DC voltage source, blocking DC voltages and providing a DC image of a connected HDMI receiver to ensure proper operation of HDMI sources and receivers, while preventing excessive voltage from reaching the TMDS lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC coupling is used to block DC voltage on the cable, then protection from excessive voltage is improved, but the HDMI source cannot operate correctly without a DC image of the receiver
Solution Approach 1:
The capacitor serves as an intermediary that simultaneously achieves two functions: blocking DC voltage to protect against excessive voltage and allowing AC coupling to pass TMDS signals. This resolves the contradiction by finding a component that can perform both protection and signal transmission without requiring additional active circuitry.
Solution Approach 2:
The protection circuit creates a DC image of the HDMI receiver using the capacitor and voltage source arrangement. This DC image mimics the electrical characteristics of a connected receiver, allowing the HDMI source to operate correctly while the capacitor blocks harmful DC voltage from the cable.
2Ease of operation
If a voltage source is coupled to the splitter to provide a DC image, then HDMI source operation is improved, but the circuit complexity increases
Solution Approach 1:
The capacitor performs multiple functions simultaneously: it blocks DC voltage, allows AC signal passage, and participates in creating the DC image. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in circuit complexity while achieving the required operational correctness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The protection circuit effectively blocks DC voltages from short circuits, ensuring the HDMI system operates correctly by mimicking a connected HDMI receiver, thus preventing damage to HDMI sources and receivers from excessive voltages, while allowing audio and video data transmission.
Implementation Method 1
a pair of capacitors, each capacitor having a first terminal and a second terminal, wherein the first terminal of each capacitor is coupled to a respective one of the pair of electrical conductors
Implementation Method 2
a pair of splitters, each splitter being coupled to a respective one of the pair of TMDS terminals and arranged to split a signal from respective one of the pair of TMDS terminals between at least two signal paths
Data Source
AI summary
HDMI devices coupled to interfaces in environments with high voltages, for example in an automotive vehicle, may be damaged by a short circuit between a cable and a large DC voltage. A protection circuit (100) for the high speed TMDS lines of an HDMI interface includes a DC voltage source (22, 24), a pair of capacitors (C1, C2) and a pair of splitters (12, 14). Each splitter is arranged to split a signal from respective one of the pair of electrical conductors between two signal paths, whereby one of the signal paths is coupled to the voltage source, and a second signal path is coupled to a first terminal of a respective one of the pair of capacitors. A signal received from an HDMI source (26) is split between a first path coupled to a first terminal of a respective capacitor and a second path coupled to the DC voltage source. The protection circuit can block a DC voltage on a cable (28) connected to the second terminals of the respective capacitors while providing a DC image of a receiver so allowing correct operation of a connected HDMI source.