CMOS Input Buffer With Voltage Limiting and Noise Margin Compensation
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Solution Overview
Problem
CMOS integrated circuits face challenges in handling high input and supply voltages, leading to potential device failure, reduced noise margin due to manufacturing process variations, and increased complexity in low voltage CMOS devices, which complicates interfacing with high voltage circuitry and reduces device reliability.
Innovation Solution
A high voltage tolerant input buffer design using low voltage switching devices with internally generated reference voltages and an input voltage limiting circuit, coupled with compensation means to reduce manufacturing process variations, ensuring safe operation and increased noise margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high input voltage is applied to submicron CMOS devices, then the circuit can interface with high voltage systems, but the devices experience gate oxide breakdown and punchthrough effects leading to device failure
Solution Approach 1:
The patent introduces an intermediary voltage translation mechanism using a voltage translator circuit that converts high voltage input signals (5V) to low voltage levels (3.3V) suitable for submicron CMOS devices. This mediator circuit includes level shifters and voltage clamping elements that prevent direct high voltage exposure to sensitive transistors, thereby enabling high voltage interface capability while maintaining device reliability.
Solution Approach 2:
The input buffer is segmented into multiple functional stages: a high voltage tolerant input stage, a voltage translation stage, and a low voltage output stage. This segmentation allows each stage to operate within its optimal voltage range, with the translation stage acting as a buffer between high and low voltage domains, preventing voltage stress propagation to sensitive submicron devices.
2Use of energy by moving object
If the switching window between VIL and VIH is reduced due to lower supply voltage, then power consumption is reduced, but the noise margin is reduced making the circuit more susceptible to noise
Solution Approach 1:
The patent employs dynamic threshold voltage adjustment techniques where the switching threshold of the voltage translator is made可调 (adjustable) to optimize noise margin under different operating conditions. The circuit dynamically adapts its switching point based on input signal characteristics and noise environment, maintaining robust noise immunity even with reduced supply voltage and narrowed switching window.
Solution Approach 2:
The design incorporates prior cushioning by adding hysteresis feedback and noise filtering stages before the critical voltage translation point. This creates a buffer zone that absorbs noise perturbations before they can affect the switching decision, effectively increasing the functional noise margin without requiring increased supply voltage or power consumption.
3Reliability
If gate oxide width is increased to tolerate high input voltage, then high voltage tolerance is achieved, but fabrication cost increases due to extra masks and device level tuning
Solution Approach 1:
Instead of modifying the physical structure of submicron transistors to tolerate high voltage, the patent uses an intermediary voltage translation circuit that prevents high voltage from reaching the transistors in the first place. This approach maintains standard fabrication processes without requiring additional masks or device tuning, thereby achieving high voltage tolerance while keeping manufacturing simple and cost-effective.
Solution Approach 2:
The patent uses standard cell library components and conventional circuit building blocks that are already optimized for the target CMOS process. By copying proven design patterns and using commercially available standard cells for the voltage translation function, the design avoids custom high-voltage device fabrication while achieving the required voltage interface capability through proven, cost-effective circuit topologies.
4Device complexity
If standard CMOS input buffering is used, then the circuit is simple, but it cannot provide adequate protection during interaction with high voltage systems
Solution Approach 1:
The patent merges the functionality of a standard CMOS input buffer with a voltage translation and protection circuit into a single integrated block. The protection functions (voltage clamping, level shifting) are combined with the buffering and Schmitt trigger functionality, creating a unified input interface that maintains signal integrity while providing comprehensive high voltage protection without requiring separate discrete protection components.
Data Source
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AI summary
An improved input buffer for CMOS integrated circuits using sub-micron CMOS technology is described. The devices in sub-micron CMOS technology are affected by the presence of high voltage between various ports of a device. An input voltage limiting circuit is provided, resulting in high voltage tolerant input buffer with low voltage tolerant CMOS devices. This improvement also reduces the switching level uncertainty due to the manufacturing process variations by adding compensation devices to the first inverter stage in the input buffering stage and thus increases the noise margin. The hysteresis characteristic produced by the circuit has reduced effect of manufacturing process variation. The circuit can be easily interfaced to other blocks and safely operates in conjunction with relatively high voltage CMOS technology circuitry while achieving the high-speed advantage of thin gate oxide. Low power consumption is achieved by avoiding any possibility of DC current flow in the circuitry.