DisplayPort Switch Precharge Circuit for Stable AUX Link Setup
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Solution Overview
Problem
Conventional DISPLAYPORT switches experience link establishment errors due to capacitors C1 and C2 charging issues, leading to voltage fluctuations on the auxiliary channel, which can result in incorrect assertion or de-assertion of the HPD channel and signal corruption during charging.
Innovation Solution
Incorporation of precharge circuits, specifically switched voltage dividers and pulling circuits, that precharge capacitors C1 and C2 to a stable voltage before enabling communication, ensuring consistent auxiliary signal levels and preventing HPD channel misinterpretation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitors C1 and C2 are used to couple the sourcing circuit and switch together, then the auxiliary channel can transmit differential signals, but voltage fluctuations occur during capacitor charging that cause link establishment errors
Solution Approach 1:
The patent applies preliminary action by pre-charging capacitors C1 and C2 to a predetermined voltage level before the switch is activated. The precharge circuits are enabled prior to switch activation to ensure capacitors reach the required voltage threshold, preventing voltage fluctuations during the critical link establishment phase when the switch transitions from off to on state.
2Ease of operation
If switches S1 and S2 are activated to enable communication between sourcing and sinking circuits, then the auxiliary channel becomes operational, but capacitors begin charging causing voltages to go outside expected ranges
Solution Approach 1:
The precharge circuits perform preliminary charging of capacitors to predetermined voltage levels before the main switches are activated. This ensures that when communication is enabled, the voltages on the auxiliary channel remain within expected ranges, maintaining voltage level precision while enabling ease of operation.
Solution Approach 2:
The precharge circuits act as intermediary circuits between the power supply and the main switch activation. They provide a controlled charging path that mediates the voltage transition, ensuring smooth voltage establishment without abrupt changes that would cause precision errors during switch activation.
3Measurement precision
If the sinking circuit measures voltages on the auxiliary channel to determine link establishment, then link status can be detected, but incorrect voltage levels lead to incorrect HPD channel assertion
Solution Approach 1:
By pre-charging capacitors to predetermined voltage levels before switch activation, the measurement precision of voltage detection is ensured. The sinking circuit can accurately measure voltages on the auxiliary channel because the precharge circuits have already established stable, expected voltage levels, leading to correct HPD channel assertion and improving reliability.
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 precharge circuits stabilize capacitor voltages, preventing link errors and signal corruption, ensuring reliable communication by maintaining auxiliary signals within expected ranges during charging, thus improving the reliability of the DISPLAYPORT switch.
Implementation Method 1
Capacitors C1 and C2 (which have a capacitance between about 75 nF to about 200 nF) are used between the souring circuit 102 and switch 132
Implementation Method 2
Voltage dividers (resistors R1/R2 and resistors R3/R4) are coupled across cables 106 and 108 (respectively) between a voltage source VDD and ground
Data Source
AI summary
In versions 1.1a and 1.2 of the DISPLAYPORT™ standard, capacitors are used between a sourcing circuit and a switch for the auxiliary channel. As a result, these capacitors are generally uncharged when the switch activates the auxiliary channel, which can result in errors. Here, a switch is employed that uses precharge circuits to precharge these capacitors. Thus, errors due to charging of these capacitors can be reduced.