Isolated DVI Receiver Grounding to Reduce EMI and Transients
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Solution Overview
Problem
Commercial DVI standards are incompatible with aerospace applications due to electromagnetic interference and transient voltage issues, as they require a DC connection between the source and load ground, creating impedance common paths that induce electromagnetic emissions and are susceptible to lightning transients, interfering with sensitive avionic systems.
Innovation Solution
An isolated DVI receiver is implemented at the load end, disconnecting the current return path through the over-braid shield and redirecting it through the internal twisted pair shields, while isolating the receiver processing circuitry from the chassis ground, maintaining compliance with commercial DVI standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC connection between source and load ground is implemented according to commercial DVI standards, then the circuit is completed and the interface functions properly, but electromagnetic emissions increase and susceptibility to lightning transients worsens
Solution Approach 1:
The patent segments the ground connection by introducing an isolated ground for the receiver processing circuitry that is electrically separated from the chassis signal ground. This segmentation breaks the common impedance path that allows electromagnetic coupling, while maintaining separate ground references for signal integrity.
Solution Approach 2:
The patent introduces an isolating interface as an intermediary element between the shielded twisted pair cables and the receiver processing circuitry. This intermediary provides galvanic isolation, blocking the transmission of electromagnetic interference and transient voltages while allowing signal transmission through magnetic coupling.
2Object-affected harmful factors
If the over-braid shield is connected to chassis ground at both ends, then shielding effectiveness is improved, but common-mode currents are induced and electromagnetic radiation increases
Solution Approach 1:
The patent extracts the receiver processing circuitry from the chassis ground reference and places it on an isolated ground. This removes the circuitry from the common-mode current path established by the over-braid shield connection, preventing the shield from acting as an antenna while maintaining its shielding function.
Solution Approach 2:
Instead of connecting the receiver ground to chassis ground as in conventional DVI, the patent inverts the approach by isolating the receiver ground from chassis ground. The isolating interface allows signal transmission while preventing the formation of common-mode current loops that cause radiation.
3Measurement precision
If balanced drive levels and equal impedance are maintained, then differential signaling is optimized, but common-mode currents still flow in the ground path through cable shields
Solution Approach 1:
The isolating interface acts as an intermediary that blocks the path for common-mode currents in the ground path through cable shields, while allowing the balanced differential signaling to pass through via magnetic coupling. This separates the signal transmission function from the ground reference function.
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
This solution reduces electromagnetic emissions and minimizes the effects of lightning-induced transients, ensuring compliance with stringent aerospace requirements without modifying the transmitter or cable design.
Implementation Method 1
The isolating interface electrically isolates the receiver processing circuitry from the chassis signal ground to which the over-braid shield is connected
Implementation Method 2
causing return current to be redirected through the twisted pair cable shields rather than the over-braid shield, thereby reducing electromagnetic emissions
Data Source
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AI summary
Digital video signals are transmitted from a transmitter to a receiver (100B) via a digital video interface including shielded twisted pair cables (200A, 200B) that are surrounded by an over-braid shield (250). The over-braid shield is connected to a chassis ground (140) at a transmitting end and the receiving end. An interface conveys the received signals to receiver processing circuitry (150). The interface is connected to an isolated ground (125B), isolating the receiver processing circuitry. Cable shields of the twisted pairs are also connected to the isolated ground (125B), such that a return current is forced back through the twisted pair cable shields rather than the over-braid shield. This reduces electromagnetic emissions and confines transients primarily to the over-braid shield.