Multifunctional Output Driver for LVDS and CML Interface Switching
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Solution Overview
Problem
Current multifunctional output drivers require multiple sets of output drivers and pre-drivers to handle different transmission interfaces, leading to increased chip area and power consumption, especially when powered by high I/O power voltages.
Innovation Solution
A multifunctional output driver design that employs two differential units, where one unit is disabled in a first transmission mode and both units are enabled in a second mode, allowing the same driver to support both low voltage differential signaling (LVDS) and current mode logic (CML) interfaces, with a pre-driver powered by a core power voltage to reduce power consumption and chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple sets of output drivers and pre-drivers are used to handle different transmission interfaces, then the driver can support both LVDS and CML interfaces, but the chip area and power consumption increase
Solution Approach 1:
The patent implements a single output driver circuit that can operate in multiple transmission modes (LVDS and CML) by using mode selection signals to configure the differential units. The first and second differential units can be selectively enabled or disabled based on the desired transmission interface, allowing one circuit to perform multiple functions that previously required separate dedicated drivers for each interface type
Solution Approach 2:
The patent combines two differential units (first and second differential units) into a single integrated output driver structure. By merging these units and using mode selection logic to activate only the required unit based on the transmission interface type, the design eliminates the need for completely separate driver circuits for LVDS and CML, thereby reducing chip area while maintaining support for both interfaces
2Adaptability or versatility
If multiple sets of output drivers and pre-drivers are used to handle different transmission interfaces, then the driver can support both LVDS and CML interfaces, but the power consumption increases
Solution Approach 1:
The patent employs dynamic mode selection where the output driver can switch between LVDS and CML transmission modes based on operational requirements. Mode selection signals dynamically configure which differential units are active, allowing the circuit to adapt its power consumption characteristics to match the actual transmission interface being used, rather than continuously powering all units regardless of mode
Solution Approach 2:
A single unified output driver structure supports both LVDS and CML interfaces through configurable operation modes. The first and second differential units are selectively activated based on the desired interface type, enabling one circuit to replace multiple dedicated circuits while reducing overall power consumption by avoiding simultaneous operation of all units
3Use of energy by stationary object
If a pre-driver powered by core power voltage is used instead of I/O power voltage, then power consumption is reduced, but the driving capability must be maintained
Solution Approach 1:
The patent changes the power supply parameter from high-voltage I/O power to lower-voltage core power for the pre-driver stage. This parameter change reduces power consumption while the differential units maintain their ability to provide sufficient driving capability for the transmission interface, as the differential architecture inherently provides good signal swing and drive strength even with lower power supply voltages
4Adaptability or versatility
If two differential units are used in the output driver, then both LVDS and CML interfaces are supported, but the device complexity increases
Solution Approach 1:
The patent segments the output driver into two functional differential units (first and second differential units) that can be independently controlled through mode selection signals. This segmentation allows each unit to be optimized for specific interface requirements while sharing common circuit resources, reducing the overall complexity compared to having fully separate driver circuits for each interface type
Data Source
AI summary
A multifunctional output driver capable of transmitting signals of different interfaces in different modes is provided, in which first and second current sources are provided, and first to fourth switching devices are coupled between the first and second current sources, and the first and second current source and the first to the fourth switching devices act as a current steering circuit. In a first transmission mode, the first and second switching devices are turned off, and the third and fourth switching devices and the first current source act as a current mode logic circuit to provide an output signal compatible with a first transmission interface according to an input signal from a pre-driver. In a second transmission mode, the current steering circuit outputs an output signal compatible with a second transmission interface according to the input signal from the pre-driver.