USB Hub Host Disconnection Detection via DM Line Sampling
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Solution Overview
Problem
USB hubs face difficulties in detecting the disconnection of a Host device when a dual role device, such as an iPad, is plugged into a downstream port, as the absence of VBUS activity cannot distinguish between suspend and disconnect states, leading to power-saving issues.
Innovation Solution
The implementation of host detection circuitry within the USB hub, utilizing a 10 uA current source and pull-up resistors on the DM connection line, allows the hub to differentiate between a suspended and disconnected Host by periodically sampling the logic level of the DM line, enabling the hub to switch back to downstream mode when disconnection is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If VBUS is always present to power the dual role device, then the device can receive power continuously, but the hub cannot distinguish between suspend and disconnect states
Solution Approach 1:
The patent introduces an intermediary detection mechanism (DM line sampling with pull-up resistors and current sources) that mediates between the always-present VBUS power signal and the hub's need to detect disconnect status. This intermediary circuit allows the hub to sense the presence or absence of the host through the DM line's electrical characteristics even when VBUS remains active.
Solution Approach 2:
The patent replaces the traditional mechanical/electrical disconnect detection method (monitoring VBUS presence) with an electrical field-based detection method (sampling DM line logic levels). This substitution allows detection to occur while maintaining continuous power supply, resolving the contradiction between power continuity and detection accuracy.
2Loss of energy
If the hub enters suspend state to save power during no activity, then energy consumption is reduced, but disconnect detection becomes impossible
Solution Approach 1:
The patent implements periodic sampling of the DM line logic level while the hub is in suspend state. This periodic detection action allows the hub to maintain power-saving mode while still reliably detecting disconnect events, as the sampling occurs at intervals sufficient to detect changes without requiring continuous active monitoring.
Solution Approach 2:
The detection circuitry uses the existing DM line and its inherent electrical characteristics (pull-up resistors, current sources) to perform self-detection during suspend state. The system serves itself by using the same communication infrastructure to detect disconnect status without requiring additional power-intensive active monitoring circuits.
3Measurement precision
If host detection circuitry continuously monitors the DM line, then disconnect detection accuracy is improved, but power consumption increases
Solution Approach 1:
The host detection circuitry performs periodic sampling of the DM line logic level rather than continuous monitoring. This periodic action maintains high detection precision by checking at sufficient intervals while dramatically reducing power consumption compared to continuous active monitoring of the communication lines.
Solution Approach 2:
The patent changes the operational parameters of the detection circuitry by using high-impedance pull-up resistors and low-current sources (10uA) that minimize power consumption while maintaining sufficient signal detection capability. The circuit parameters are optimized to achieve accurate logic level detection with minimal energy expenditure.
Data Source
AI summary
A USB hub includes a plurality of downstream ports; at least one dual mode port, the dual mode port configured to be switchable from a downstream port to an upstream port; and host detection circuitry for detecting whether, when operating as an upstream port, a host is connected.