Common-Mode Driver Circuit for Low-Power Serial Transmitters
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Solution Overview
Problem
Existing I/O interfaces face challenges in maintaining common-mode voltage efficiency while operating in low-power modes, as voltage dividers consume power and are inefficient in driving current, and partially operating CML output driver circuits dissipate power to maintain voltage levels, leading to inadequate performance and high power consumption.
Innovation Solution
A method and apparatus that include a common mode driver and data output driver circuit configured to maintain a common mode voltage during low power states and switch to differential voltage levels when not in low power states, using a reference voltage circuit to manage power efficiently, allowing precise voltage control and reduced power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage divider is used to maintain common-mode voltage in low-power mode, then the common-mode voltage is maintained, but power consumption increases and current driving capability is insufficient
Solution Approach 1:
The patent extracts the common-mode voltage maintenance function from the traditional voltage divider approach and implements it through a dedicated common-mode driver circuit that operates independently during low-power modes, eliminating the need for continuous operation of the main CML output driver circuit while maintaining precise VCM control
Solution Approach 2:
The patent changes the operational parameters by switching between different circuit configurations: during low-power modes, only the common-mode driver operates with optimized current levels, while during active modes, the full CML output driver circuit operates at higher current levels, dynamically adjusting power consumption based on operational requirements
2Reliability
If a voltage divider is used to maintain common-mode voltage, then the circuit remains operational, but current driving capability is weak causing large VCM errors
Solution Approach 1:
The patent implements dynamic parameter adjustment by changing the output current levels of the common-mode driver based on operational mode. During low-power modes, the driver operates at reduced current levels optimized for VCM maintenance, while during active modes, it switches to higher current levels that provide both VCM control and sufficient driving capability to minimize leakage-induced errors
3Reliability
If partially operating CML output driver circuit is used to maintain voltage levels, then the output voltage is maintained, but power dissipation increases consuming over 3 mA
Solution Approach 1:
The patent segments the CML output driver circuit into two independent functional blocks: a common-mode driver portion dedicated to VCM control and a data output driver portion for differential signal transmission. This segmentation allows the common-mode driver to operate independently at low power during low-power modes, maintaining output voltage levels without requiring the entire circuit to remain active, thereby dramatically reducing power dissipation
Solution Approach 2:
The patent implements periodic action by switching between different operational states: during low-power modes, only the common-mode driver portion operates periodically to maintain VCM levels, while the data output driver portion remains inactive; during active modes, both portions operate simultaneously, providing full functionality with power consumption optimized for each operational phase
4Reliability
If bias circuits remain powered on to maintain operation, then the circuit functionality is preserved, but power consumption increases
Solution Approach 1:
The patent extracts the bias circuit functionality and integrates it specifically within the common-mode driver portion, allowing the bias circuits to remain powered on only when needed for common-mode voltage control during low-power modes, while the data output driver portion can be completely powered down, eliminating unnecessary power consumption from redundant bias circuit operation
Solution Approach 2:
The patent segments the bias circuitry into two separate sets: one set dedicated to the common-mode driver portion and another set for the data output driver portion. This segmentation enables independent power management where the common-mode driver's bias circuits remain active during low-power modes to maintain VCM stability, while the data output driver's bias circuits can be completely disabled, optimizing overall power dissipation
Data Source
AI summary
A method is provided for controlling a data transmission device. The method includes providing a reference voltage to the common mode driver and putting the data transmission device in a low power state. The method also includes driving a differential signal pair output from the common mode driver during a portion of the low power state. Also provided is a device that includes a data output driver portion configured to drive an output signal at a common mode voltage and a data output driver portion configured to drive an output signal at a differential voltage level during at least a portion of time when the device is not in a low power state. Also provided is a computer readable storage device encoded with data for adapting a manufacturing facility to create the device. Also provided is an apparatus configured to perform the method.