LVDS Input Circuit for Single-Pair Bidirectional Signaling
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Solution Overview
Problem
Conventional Low Voltage Differential Signaling (LVDS) interfaces require double the number of connections for simultaneous communication between sending and receiving circuits, limiting their application and increasing noise susceptibility due to reduced termination resistance.
Innovation Solution
Design of LVDS drivers and receivers that enable simultaneous communication over a single pair of signal paths using a network of resistors and specialized input circuits, including inverters, differential receivers, window comparators, and multiplexers, to maintain appropriate signaling voltages and noise margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional LVDS signaling is used for bidirectional communication, then communication capability is achieved, but the number of connections required doubles
Solution Approach 1:
The patent combines send and receive functions into a single LVDS interface by merging the transmission and reception pathways. The input circuit integrates multiple functions (differential receiver, inverter, window comparator, multiplexer) to enable bidirectional communication over a single pair of signal paths, eliminating the need for separate connection pairs for each direction.
Solution Approach 2:
The LVDS interface is designed with multi-functionality to handle both sending and receiving operations through the same physical connections. The input circuit can selectively route signals based on operation mode (send or receive), making the single interface universal for bidirectional communication rather than requiring dedicated paths for each function.
2Quantity of substance
If a single pair of signal paths is used for bidirectional communication, then connection requirements are reduced, but noise immunity deteriorates due to reduced termination resistance
Solution Approach 1:
The termination resistance is made dynamic rather than fixed. The circuit selectively switches between a first termination resistance value (optimized for receive mode noise immunity) and a second termination resistance value (optimized for send mode signal drive) based on the operational state. This dynamic adjustment maintains optimal noise immunity during reception while enabling proper signal transmission during sending operations.
Solution Approach 2:
The patent changes the termination resistance parameter based on operational requirements. By switching between different resistance values depending on whether the interface is sending or receiving, the system optimizes both noise immunity during reception and signal drive capability during transmission, resolving the contradiction between reduced connections and maintained noise immunity.
Data Source
AI summary
First and second devices may simultaneously communicate bidirectionally with each other using only a single pair of LVDS signal paths. Each device includes an input circuit and a differential output driver connected to the single pair of LVDS signal paths. An input to the input circuit is also connected to the input of the driver. The input circuit may also receive an offset voltage. In response to its inputs, the input circuit in each device can use comparators, gates and a multiplexer to determine the logic state being transmitted over the pair of LVDS signal paths from the other device. This advantageously reduces the number of required interconnects between the first and second devices by one half.