USB Bus Switch Circuit for HS Signal Integrity and Disconnect Detection
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Solution Overview
Problem
USB signal degradation due to parasitic capacitance and resistance in USB HS mode transmission circuits, making it difficult to pass EYE pattern authentication tests and detect device disconnection, especially in long cables or with protection circuits present.
Innovation Solution
A circuit device with a bus switch circuit that connects and disconnects USB buses based on monitoring results from a bus monitor circuit, improving signal characteristics and enabling device disconnection detection through packet bit resynchronization and disconnection detection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transmission signals are output through a cable harness or protection circuit in HS mode, then data transfer function is achieved, but signal characteristics degrade due to parasitic capacitance and resistance
Solution Approach 1:
The patent introduces a bus switch circuit as an intermediary component between the USB host and device. This switch circuit can selectively connect or disconnect the bus, allowing the system to bypass protection circuits or long cable paths that cause signal degradation. By using the bus switch as a mediator, the system can choose optimal signal paths that minimize parasitic effects while maintaining data transfer functionality.
Solution Approach 2:
The patent implements dynamic switching of the USB bus connection state based on operational requirements. The bus switch circuit dynamically transitions between connected and disconnected states, enabling the system to adapt signal paths in real-time. This dynamic behavior allows bypassing of degraded paths during data transfer while enabling disconnection detection during idle periods, resolving the contradiction between maintaining signal quality and detecting device status.
2Productivity
If the bus connection is maintained for data transfer, then productivity is improved, but device disconnection detection becomes difficult
Solution Approach 1:
The patent employs periodic monitoring of the USB bus state through the bus switch circuit. The circuit periodically checks for device presence by monitoring bus electrical characteristics during idle periods or at designated intervals. This periodic action enables reliable disconnection detection without interfering with continuous data transfer operations, as the monitoring occurs in a time-multiplexed manner that does not disrupt productivity-critical data transmission.
Solution Approach 2:
The bus switch circuit incorporates feedback mechanisms that monitor bus state and provide information about device connection status. The circuit detects changes in bus electrical characteristics (such as pull-up resistor states) and generates feedback signals indicating device presence or disconnection. This feedback system enables the host to reliably detect device disconnection while maintaining continuous data transfer, as the feedback is derived from passive monitoring of existing bus signals rather than active interruptions.
3Reliability
If protection circuits are added to the signal path, then reliability against electrical disturbances is improved, but signal transfer capability degrades
Solution Approach 1:
The patent segments the USB signal path into multiple controllable sections using the bus switch circuit. By dividing the connection path into switchable segments, the system can isolate protection circuits from the active signal transmission path when needed. The bus switch creates distinct operational segments: one path through protection circuits for protected operation, and another bypass path for high-quality signal transfer when protection is not required, thus resolving the contradiction between protection and signal quality.
Data Source
AI summary
A circuit device includes: a first physical layer circuit to which a first bus compliant with a USB standard is connected; a second physical layer circuit to which a second bus compliant with the USB standard is connected; a processing circuit that performs transfer processing in which a packet received from the first bus via the first physical layer circuit is transferred to the second bus via the second physical layer circuit, and a packet received from the second bus via the second physical layer circuit is transferred to the first bus via the first physical layer circuit; a bus monitor circuit that performs a monitor operation with respect to the first and second buses; and a bus switch circuit that switches on or off a connection between the first bus and the second bus based on a monitor result from the bus monitor circuit.