Open-Drain Output Interface With Common-Mode Bulk Biasing
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Solution Overview
Problem
Impedance mismatch between open-drain output drivers and transmission lines in portable wireless devices leads to reflection loss and reduced transmission power, particularly in high-speed applications like HDMI compliant transmitters.
Innovation Solution
An output interface with a common mode connection coupled to a transistor bulk connection, utilizing a resistor network controlled by transistors to adjust the output impedance of open-drain drivers, ensuring reliability even when operating at lower supply voltages compared to the receiver side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the output driver operates at a lower supply voltage to enable lower power operation, then power consumption is reduced, but transistor reliability deteriorates when coupled to a higher voltage receiver
Solution Approach 1:
The bulk connection acts as an intermediary voltage reference that is coupled to the common mode connection. This intermediary structure allows the transistor to operate reliably by providing a stable voltage reference point that accounts for the voltage difference between the low-voltage driver side and high-voltage receiver side, preventing voltage stress on the transistor while enabling lower power operation
2Device complexity
If the output impedance is not adjusted to match the transmission line, then device complexity is reduced, but transmission power is lost due to reflection loss
Solution Approach 1:
The output impedance is made dynamically adjustable through a resistor network that can be selectively connected or disconnected based on operating conditions. This dynamic adjustment allows the driver to match the transmission line impedance when needed to minimize reflection loss, while maintaining a simpler default configuration when impedance matching is not required, thus balancing complexity and performance
Data Source
AI summary
A multi-terminal output with a common mode connection includes an output having a first terminal and a second terminal and having a common mode connection between the first terminal and the second terminal. A bulk connection of a transistor is coupled to the common mode connection. A first set of control signals and a second set of control signals are generated. Each of the first set of control signals has a first rail voltage level associated with a first power domain. The second set of control signals is generated from the first set of control signals. Each of the second set of control signals has a second rail voltage level that is associated with a second power domain. The second power domain is associated with a common mode voltage of outputs of an output driver.