LVDS Driver Branch Resistor Symmetry for Half-Duplex Signaling
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Solution Overview
Problem
Conventional low voltage differential signaling drivers face issues with signal reflections and power consumption, and are limited in adopting a half-duplex structure due to asymmetrical termination resistor configurations, which increases the number of pins required for signal transmission and reception.
Innovation Solution
The proposed low voltage differential signaling driver incorporates a symmetrical configuration with series-connected transistors and resistors in both transmission and reception units, allowing for equal termination resistance on both sides and minimizing signal reflections, while using a control switch to adjust resistance for reduced power consumption and half-duplex capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If termination resistors are connected in parallel in the transmission unit, then signal reflection is reduced, but power consumption increases significantly
Solution Approach 1:
The termination resistance is segmented into multiple resistors connected in series within each branch circuit. Instead of using a single parallel termination resistor that consumes high power, the patent divides the termination function into series-connected resistors (e.g., two 50Ω resistors in series to achieve 100Ω termination) that are only activated during reception mode, thereby reducing power consumption during transmission while maintaining signal reflection reduction.
Solution Approach 2:
The termination resistor configuration is made dynamic through the use of switches that can connect or disconnect the termination resistors based on whether the device is in transmission or reception mode. During transmission, the termination resistors are disconnected to minimize power consumption. During reception, they are connected to reduce signal reflection. This dynamic switching resolves the contradiction between power consumption and signal reflection reduction.
2Device complexity
If asymmetrical termination resistor configuration is used, then signal transmission is simplified, but the number of pins increases and half-duplex capability is lost
Solution Approach 1:
The patent employs asymmetrical termination resistor configuration where the transmission unit and reception unit have different termination arrangements. The transmission unit uses series-connected resistors while the reception unit uses parallel-connected resistors, allowing simplified signal transmission in each direction while maintaining the ability to switch between transmission and reception modes for half-duplex operation.
Solution Approach 2:
The same physical pins are made universal by implementing half-duplex capability through controlled switching. The transmission and reception units share the same pin assignments, and through the use of switches that control the activation of respective transmission and reception circuits, the system can function in both transmission and reception modes using the same pins, thereby reducing pin count while maintaining versatility.
3Reliability
If high current is used to maintain voltage difference, then signal transmission quality is improved, but power consumption increases
Solution Approach 1:
The system uses periodic switching between transmission and reception modes rather than continuous high-current operation. During transmission mode, high current flows to maintain voltage difference and ensure signal quality. During reception mode, the current is reduced or stopped, and termination resistors are activated instead. This periodic action maintains signal transmission quality when needed while minimizing power consumption during reception.
Solution Approach 2:
The system changes operational parameters (current level, resistance configuration) based on the operating mode. In transmission mode, high current and low termination resistance are used to ensure signal quality. In reception mode, low current and high termination resistance are used to minimize power consumption while maintaining acceptable signal reception. This dynamic parameter adjustment resolves the contradiction between signal quality and power consumption.
Data Source
AI summary
A low voltage differential signal driver includes first and second current sources, a first branch and a second branch. The first branch includes at least two transistors and at least two resistors between them that are all connected in series between the first and second current sources, to define a first node between adjacent resistors that is configured to transmit and receive differential signals. The second branch also includes at least two transistors and at least two resistors between them that also are all connected in series between the first and second current sources, to define a second node between adjacent resistors that is also configured to transmit and receive differential signals.