High-Speed Transceiver Common-Mode Voltage Control
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Solution Overview
Problem
Repeater designs in serial data transmission systems face challenges in maintaining the instantaneous voltage within the specified range during power-down conditions, particularly due to the discharge rate of the supply voltage, which can cause the downstream voltage to drop below the minimum allowed by the USB standard, especially in systems lacking additional GPIO pins for controlled power-off sequences.
Innovation Solution
Incorporating a load voltage control circuitry that detects a supply voltage drop and transitions the transmit node to a high impedance state, disconnecting an external capacitor from the supply voltage node to ensure the instantaneous voltage remains within the specified range, using a comparator and power control circuitry to manage the power-down sequence and capacitor discharge rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the supply voltage discharge rate is increased during power-down, then the power-down speed is improved, but the downstream instantaneous voltage drops below the minimum allowed by the USB standard
Solution Approach 1:
The transmit node is transitioned to a high impedance state before the supply voltage discharge begins. This preliminary action prevents the downstream instantaneous voltage from dropping below the minimum allowed by the USB standard during the power-down sequence, allowing faster voltage discharge without violating compliance requirements.
2Reliability
If a controlled power-off sequence is implemented, then the voltage range compliance is improved, but the device complexity increases due to additional GPIO pins
Solution Approach 1:
The repeater autonomously manages its power-down sequence by internally transitioning the transmit node to a high impedance state when detecting the power-down condition. This self-service approach eliminates the need for external GPIO pins to control the power-off sequence, reducing device complexity while maintaining voltage range compliance.
3Device complexity
If the transmit node remains connected to the supply voltage during power-down, then the voltage control is simplified, but the downstream instantaneous voltage violates the USB standard
Solution Approach 1:
The transmit node is disconnected from the supply voltage by transitioning to a high impedance state before the supply voltage discharge begins. This preliminary disconnection prevents the downstream instantaneous voltage from dropping below the USB standard minimum, ensuring compliance without requiring complex control circuits.
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 effectively maintains the instantaneous voltage within the USB-standard-specified range, preventing violations during power-down conditions without requiring additional GPIO pins, ensuring compliance with the USB standard and optimizing system design.
Implementation Method 1
an external capacitor connected to a transmit output of the repeater
Data Source
AI summary
Circuits and techniques are described for high-speed transceivers (e.g., repeaters such as re-drivers or re-timers) that ensure that the instantaneous voltage at an input or output of a connected device remains within a desired or specified voltage range.