Bidirectional interface apparatus and method for operating the same
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Solution Overview
Problem
Existing interface circuits for low voltage core devices face challenges in minimizing signal reflections and voltage stresses, leading to reduced signal integrity and increased bit error rates, especially when interfacing with higher voltage legacy systems.
Innovation Solution
A bidirectional differential interface with a voltage-mode transmit driver architecture featuring multiple selectively enabled slices for impedance matching, programmable resistance, and proactive voltage protection to minimize voltage stresses, allowing operation at low core voltages while ensuring compatibility with higher voltage devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If termination resistors are employed to minimize reflections and improve signal integrity, then bit error rate decreases and transmission distance increases, but device complexity and power consumption increase
Solution Approach 1:
The patent combines the transmit driver and receive buffer into a single bidirectional interface apparatus sharing common differential output nodes. The termination resistors are integrated within the transmit driver circuitry, merging multiple functions (transmitting, receiving, and termination) into one unified structure, thereby reducing overall device complexity while maintaining signal integrity
Solution Approach 2:
The bidirectional interface apparatus serves multiple functions: it acts as a transmitter during transmit mode and as a receiver during receive mode, with the same physical interface and termination resistors serving both purposes. This multi-functionality eliminates the need for separate dedicated transmit and receive circuits, reducing device complexity while maintaining reliable signal transmission and reception
2Use of energy by moving object
If low core voltage is used to reduce power consumption, then power efficiency improves, but voltage stress protection becomes critical when interfacing with higher voltage legacy systems
Solution Approach 1:
The patent introduces a voltage-level mediation mechanism where the bidirectional interface apparatus with its internal termination resistors and differential signaling architecture acts as an intermediary between the low-voltage core device and higher-voltage legacy systems. The differential signaling and internal voltage regulation protect the low-voltage transistors from direct exposure to high voltage stresses while enabling communication with higher voltage devices
Solution Approach 2:
The patent implements protective measures in advance by designing the bidirectional interface with controlled impedance termination and differential signaling architecture that inherently protects against voltage stresses before they can damage the low-voltage transistors. The termination resistors and differential structure serve as pre-established protection mechanisms against potential voltage mismatches and transient overvoltages from legacy systems
3Device complexity
If bidirectional interface is implemented to reduce pin count, then device integration improves, but impedance matching and signal reflections become more challenging
Solution Approach 1:
The patent applies local quality by implementing termination resistors specifically at the output nodes of the transmit driver where impedance matching is most critical. The differential signaling structure provides localized impedance control at the interface points, ensuring proper signal transmission while allowing the rest of the low-voltage core to operate without complex impedance management
Solution Approach 2:
The patent utilizes parameter changes by making the termination resistor values programmable or selectable to match different transmission line impedances. This allows the bidirectional interface to adapt to various external systems with different impedance requirements, achieving proper impedance matching while maintaining the space-saving bidirectional architecture
Data Source
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AI summary
Methods and apparatus relate to a bidirectional differential interface (300) having a voltage-mode transmit driver architecture (325) formed of multiple selectively enabled slices for coarse output resistance impedance matching. In examples, the transmit driver (325) may include a programmable resistance (340) for fine-tuning to impedance match the output resistance for transmit operation. During receive operation, protective voltage may be proactively applied to gates of drive transistors to minimize voltage stresses applied by external signal sources. Some implementations may automatically float the sources of the drive transistors to prevent back-feeding externally driven signal currents during receive mode operations. The transmit driver (325) may have programmable voltage swing on, for example, the upper and/or lower bounds to enhance compatibility. A programmable common mode voltage node may be selectively applied in a termination network (335), for example, through common mode resistors for receive mode operations.