Bidirectional Inverter Circuit for IO-Link Master-Slave Compatibility
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Solution Overview
Problem
There is a need for a circuit arrangement that enables bidirectional communication between an IO-link compatible master device and an IO-link non-compatible slave device, specifically between a master using a push-pull circuit and a slave with a low side open collector switching transistor, as existing technologies do not support direct communication due to compatibility issues.
Innovation Solution
The proposed circuit arrangement includes a bidirectional inverter circuit with a pull-up resistor, AB class transistor circuit, current mirrors, and a bias circuit, which interfaces signals and logic behavior between the IO-link master and slave, using a comparator to manage currents and voltages, allowing the slave with a low side switch to communicate with the IO-link master.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a low side current switch (open collector NPN transistor) is used in the slave device, then the slave device structure is simpler and more cost-effective, but the slave device becomes incompatible with IO-link master devices requiring push-pull configuration
Solution Approach 1:
An interface circuit is introduced as an intermediary between the IO-link master and the non-compatible slave device. This interface circuit contains a bidirectional inverter that converts the push-pull signals from the master into low-side switch signals for the slave, and vice versa, enabling communication between incompatible devices without modifying the slave's simple structure
Solution Approach 2:
The interface circuit is divided into separate functional blocks: a pull-up resistor circuit for voltage level adjustment, an AB class transistor circuit for bidirectional signal inversion, current mirrors for signal isolation and level shifting, and a bias circuit for proper transistor operation. This segmentation allows each block to perform its specific function optimally while working together to solve the compatibility problem
2Speed
If a push-pull circuit with high side current source is used in the master device, then the master device achieves high speed communication capability, but the master device cannot directly interface with slaves using low side current switches
Solution Approach 1:
The bidirectional inverter in the interface circuit acts as a mediator that preserves the high-speed push-pull operation of the master while adapting signals for the slave. The AB class transistor circuit with current mirrors enables fast signal transitions in both directions, maintaining communication speed while providing interface compatibility
Solution Approach 2:
The interface circuit changes the electrical parameters of the signal, specifically the voltage levels and current directions. The pull-up resistor adjusts voltage levels, while the current mirrors transform current directions and magnitudes, allowing the master's push-pull signals to be properly interpreted by the slave's low-side switch and vice versa
3Adaptability or versatility
If bidirectional signal inversion is implemented between master and slave, then compatibility is achieved, but the circuit complexity increases with multiple transistor circuits and current mirrors
Solution Approach 1:
Multiple functions are merged into a single integrated interface circuit block. The bidirectional inverter combines signal inversion, voltage level adjustment, current direction transformation, and signal isolation functions into one compact circuit, reducing overall system complexity despite the sophisticated internal structure
Solution Approach 2:
The interface circuit is designed as a universal solution that can handle bidirectional signal inversion for different signal levels and current configurations. The AB class transistor circuit with current mirrors provides a multi-functional platform that adapts to various master-slave configurations while maintaining a relatively simple external interface
Data Source
AI summary
An inverter circuit arrangement that connects an IO-link master with a slave includes an AB class transistor circuit of which the currents are replicated by a current mirror to a terminal of the slave. A bias circuit provides bias voltages to the AB class transistors. A comparator forms a feedback between the master and slave terminals. The circuit provides for a bidirectional inversion to make a slave device IO-link compatible.