Low-Voltage Interface Circuit With Drain Clamping Level Shifting
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Solution Overview
Problem
Low voltage transistors in integrated circuits experience gate oxide degradation and breakdown when exposed to high voltage signals, leading to performance issues and circuit failure, particularly due to the overstressing of thinner gate oxides, and existing solutions require additional high voltage transistors and power supplies, complicating the design and increasing complexity.
Innovation Solution
The implementation of a current sense amplifier within a low voltage interface circuit that clamps the voltage levels at the drain terminals of low voltage transistors to a high level, avoiding gate oxide degradation and eliminating the need for level clipping circuits and high voltage transistors, thereby using only low voltage transistors and a single low voltage power supply to translate high input voltages into low output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If low voltage transistors are used to accommodate lower internal power supply voltages, then power consumption is reduced and integration is improved, but gate oxide degradation and breakdown occur when exposed to high voltage signals
Solution Approach 1:
A level shifting circuit is introduced as an intermediary component between the high voltage input signal and the low voltage transistor. This level shifter translates the high voltage signal to a compatible low voltage level before it reaches the transistor gate, preventing direct exposure to damaging high voltages while maintaining signal integrity and enabling the low voltage transistor to operate reliably
Solution Approach 2:
The voltage level parameter of the input signal is changed through the level shifting circuit. The circuit transforms the high voltage signal parameter into a low voltage parameter that is safe for the low voltage transistor, allowing the transistor to process external high voltage signals without experiencing gate oxide degradation
2Reliability
If level clipping circuits or high voltage transistors are added to protect low voltage transistors, then gate oxide degradation is prevented, but device complexity increases
Solution Approach 1:
The level shifting circuit is designed to perform multiple functions: it translates voltage levels, protects the low voltage transistor from high voltage damage, and interfaces between different voltage domains. By consolidating these functions into a single circuit block, the design avoids the need for separate protection circuits or high voltage transistors, thereby reducing overall device complexity while maintaining reliability
Data Source
AI summary
An improved interface circuit is provided herein for translating a relatively high input voltage into a relatively low output voltage using only low voltage transistors and a single, low voltage power supply. According to one embodiment, the interface circuit includes a power supply, a pair of input transistors with source terminals coupled together for receiving a relatively low voltage from the power supply, and a current sense amplifier with a pair of input terminals, each coupled to a drain terminal of a different one of the pair of input transistors for receiving a pair of differential currents and for generating a pair of differential voltages therefrom.