CMOS Input Buffer With Voltage Limiting and Hysteresis
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Solution Overview
Problem
Modern CMOS integrated circuits face challenges in handling high input and supply voltages, leading to potential device failure and reduced noise margin due to gate oxide stress and manufacturing process variations, especially with the increasing complexity and shrinking device dimensions in sub-micron technology.
Innovation Solution
A high-speed input buffer design using internally generated reference voltages and a multistage circuit with parallel connected inverters and compensation devices to limit input voltage and reduce manufacturing process variations, ensuring safe operation and low power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high input voltage is applied to sub-micron CMOS devices, then the circuit can interface with high voltage systems, but the gate oxide breaks down and punchthrough effect occurs causing device failure
Solution Approach 1:
The patent introduces an intermediary voltage translation mechanism using a series of inverters with progressively adjusted threshold voltages. This inverter chain acts as a mediator between the high voltage input signal and the low voltage sub-micron CMOS circuitry,逐步 translating the voltage levels to prevent direct high voltage exposure to sensitive devices
Solution Approach 2:
The patent changes the threshold voltage parameter of inverters along the signal path. By using inverters with progressively lower threshold voltages from input to output, the signal voltage is gradually reduced from high voltage levels to safe low voltage levels, preventing gate oxide breakdown while maintaining signal integrity
2Use of energy by moving object
If the switching window between VIL and VIH is reduced to minimize noise margin, then power consumption decreases, but the noise margin is further reduced making the circuit more susceptible to noise
Solution Approach 1:
The patent dynamically adjusts the switching thresholds of inverters along the signal path. Each inverter is designed with specific threshold voltage characteristics that adapt to the local voltage conditions, creating optimal noise margins at each stage while maintaining overall low power consumption through efficient voltage translation
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 is required
Solution Approach 1:
Instead of changing the physical gate oxide width parameter, the patent changes the electrical threshold voltage parameter through circuit design. Standard CMOS devices with fixed gate oxide dimensions are used, but the effective voltage tolerance is enhanced through the inverter chain's progressive voltage translation mechanism
Solution Approach 2:
The patent uses multiple copies of standard CMOS inverters with different threshold voltage characteristics arranged in series. Rather than modifying individual devices, it replicates the voltage translation function across multiple standard device copies, avoiding the need for custom high-voltage device fabrication
Data Source
AI summary
An input buffer for CMOS integrated circuits using sub-micron CMOS technology is affected by the presence of high voltage between various ports of a device. An improvement for such a buffer provides an input voltage limiting circuit making the device mode tolerant to high voltages while using low voltage tolerant CMOS devices. This improvement also reduces the switching level uncertainty due to manufacturing process variations by adding compensation devices to a first inverter stage in the input buffering stage so as to increase noise margin. A hysteresis characteristic is produced by the circuit thus reducing the 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 the possibility of DC current flow in the circuitry.