Test Board Bypass Circuit for eDP RF Noise Measurement
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Solution Overview
Problem
Measuring RF noise in display devices using the eDP interface is challenging when the sink device is turned off, as the source device and its cables do not operate normally, making it difficult to assess RF noise levels during the development process.
Innovation Solution
A test board with a bypass circuit is used between the source and sink devices, which supplies power to the hot plug detect (HPD) input terminal after a delay and includes switches to control the power supply to the sink device and backlight, allowing for normal operation of the source device even when the sink device is turned off, enabling RF noise measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the sink device is turned off to save power or during development testing, then power consumption is reduced or measurement flexibility is improved, but the source device cannot operate normally and RF noise measurement becomes difficult
Solution Approach 1:
The power supply circuit is segmented into multiple independent paths: a first power supply path for the source device and a second power supply path for the sink device. This allows the source device to be powered independently through the bypass circuit while the sink device remains powered off, enabling RF noise measurement without requiring the sink device to be operational.
Solution Approach 2:
A bypass circuit acts as an intermediary between the power supply and the source device, providing a separate power delivery path that does not depend on the sink device being powered. The bypass circuit includes a bypass switch and bypass capacitor that can be controlled independently to supply power to the source device even when the sink device is off.
2Ease of manufacture
If the sink device is turned off during development, then development flexibility and cost reduction are improved, but the source device including cables cannot operate normally making RF noise measurement difficult
Solution Approach 1:
The power distribution system is divided into independent segments allowing the source device to be powered through the bypass circuit without requiring the sink device to be powered. This segmentation enables development testing where the sink device can remain off while the source device operates for measurement purposes.
Solution Approach 2:
The bypass circuit is pre-configured with a bypass switch and bypass capacitor that can be activated before measurement begins. This preliminary setup ensures that when measurement is needed, the source device can be powered independently without requiring the sink device to be turned on first.
3Measurement precision
If a bypass circuit is added to enable independent power supply to source device, then RF noise measurement capability is improved, but device complexity increases
Solution Approach 1:
The bypass circuit extracts the power supply function for the source device from the main power distribution path that goes through the sink device. By separating this function into an independent bypass path with its own switch and capacitor, the circuit enables measurement capability while adding minimal complexity compared to redesigning the entire power system.
Data Source
AI summary
A test board between a first connector of a cable extending from a source device and a second connector of a sink device including a display panel, includes: a bypass circuit, the bypass circuit to supply a first power from a first output terminal of the first connector to a hot plug detect (HPD) input terminal of the first connector, the first power including a HPD signal.