Mixed-Voltage I/O Buffer With Dynamic Gate Control for Hot-Carrier Protection
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Solution Overview
Problem
Conventional mixed-voltage I/O buffers face issues with hot-carrier degradation, current leakage, and gate oxide reliability due to high voltage signals exceeding maximum operating voltages, especially in deep sub-micron technologies with short channel length transistors.
Innovation Solution
A mixed-voltage I/O buffer design incorporating two NMOS transistors and a dynamic gate-controlled circuit, along with a voltage slew-rate control output circuit, to manage voltage transitions and prevent excessive drain-source voltages, thereby mitigating hot-carrier degradation and current leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the I/O buffer receives a higher voltage signal (2×VDD) to interface with earlier stage CMOS circuits, then compatibility and adaptability are improved, but the drain-source voltage exceeds the maximum operating voltage causing hot-carrier degradation and reliability issues
Solution Approach 1:
The patent introduces an intermediary voltage translation mechanism using level shifters and controlled voltage domain separation. The I/O buffer creates an intermediate voltage domain that translates between the higher external voltage (2×VDD) and the lower internal operating voltage (VDD), preventing direct exposure of core transistors to excessive voltages while maintaining compatibility with external high-voltage signals
Solution Approach 2:
The patent segments the I/O buffer into distinct voltage domains: a high-voltage input stage that accepts 2×VDD signals, a voltage translation stage that converts between voltage levels, and a low-voltage output stage that operates at VDD. This segmentation isolates sensitive transistors from harmful high voltages while preserving adaptability to external high-voltage interfaces
2Productivity
If thinner gate-oxide transistors are used to achieve high-speed operation and low power consumption, then speed and energy efficiency are improved, but the transistors become more susceptible to hot-carrier-induced degradation
Solution Approach 1:
The patent dynamically changes the operating parameters of transistors by adjusting gate voltages and bias conditions. During voltage transitions, the patent modifies the gate-source and gate-drain voltages of critical transistors to keep them within safe operating ranges, preventing hot-carrier injection into the gate oxide even when using thin-oxide high-speed transistors
3Speed
If the NMOS transistor is turned on during voltage transition to pull down the source voltage, then the output signal transmission speed is improved, but the drain-source voltage becomes larger than the maximum operating voltage causing hot-carrier degradation
Solution Approach 1:
The patent applies preliminary action by pre-charging or pre-discharging relevant nodes and pre-positioning transistors in appropriate states before the actual voltage transition occurs. This preparation ensures that when the NMOS transistor turns on to pull down the source voltage, the drain voltage is already at a safe level, preventing excessive drain-source voltage and hot-carrier degradation while maintaining fast transition speed
Solution Approach 2:
The patent employs feedback mechanisms to monitor voltage levels during transitions and dynamically control transistor switching. When the source voltage approaches dangerous levels, feedback signals adjust the gate voltages of protecting transistors to limit the drain-source voltage across critical transistors, ensuring reliable operation during high-speed voltage transitions
Data Source
AI summary
A mixed-voltage I/O buffer comprises an input circuit, an output circuit, an I/O pad, a pre-driver circuit coupled to the output circuit, two added coupled N-type transistors, and a dynamical gate-controlled circuit coupled to each gate of the two N-type transistors and the pre-driver circuit; one of the N-type transistors is coupled to the input circuit and the output circuit; the other N-type transistor and the dynamic gate-controlled circuit are together coupled to the I/O pad. Thereby, a mixed-voltage I/O buffer which receives 2×VDD-tolerant input signals and overcomes the hot-carrier degradation is realized.