CMOS Voltage Clamp With Positive Feedback for Fast ESD Protection
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Solution Overview
Problem
CMOS circuits are vulnerable to damage from electrostatic discharge (ESD) events due to their design limitations, which can cause PN junction and oxide failures, and existing ESD protection circuits are costly and complex due to their large size and requirement for specialized devices.
Innovation Solution
A voltage clamp circuit using stacked transistors and a positive feedback loop is implemented between the power supply and ground to limit voltage and reduce the turn-on time of transistors, providing a discharge path and protecting CMOS circuits from ESD events without the need for special high-voltage transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ESD protection circuits are implemented using traditional methods, then ESD damage is prevented, but circuit area increases and cost increases due to specialized devices
Solution Approach 1:
The patent applies universality by using standard CMOS transistors that serve dual purposes: normal circuit operation and ESD protection. The protection circuit uses the same transistor technology as the main logic, eliminating the need for specialized high-voltage devices. This multi-functional approach allows the circuit to maintain ESD protection capabilities while avoiding the area and cost penalties of dedicated protection devices.
Solution Approach 2:
The protection circuit employs self-service through positive feedback mechanisms where the ESD event itself triggers the protection response. When ESD voltage exceeds the threshold, the circuit automatically activates the discharge path through feedback loops that turn on the protection transistors without external intervention. This self-activating mechanism ensures rapid response to ESD events while maintaining simplicity in the overall circuit design.
2Reliability
If ESD protection circuits are implemented using traditional methods, then ESD damage is prevented, but fabrication cost increases due to specialized devices
Solution Approach 1:
The patent applies universality by using standard CMOS transistors that serve dual purposes: normal circuit operation and ESD protection. The protection circuit uses the same transistor technology as the main logic, eliminating the need for specialized high-voltage devices. This multi-functional approach allows the circuit to maintain ESD protection capabilities while avoiding the area and cost penalties of dedicated protection devices.
Solution Approach 2:
The patent applies homogeneity by ensuring all transistors in the circuit, including protection transistors, are fabricated using the same CMOS process technology. This uniformity in device characteristics simplifies the fabrication process, allows for consistent process control, and eliminates the need for separate high-voltage device fabrication steps, thereby reducing manufacturing complexity and cost.
3Area of moving object
If device geometries are shrunk to improve integration, then circuit density increases, but susceptibility to ESD damage increases
Solution Approach 1:
The patent applies segmentation by dividing the protection function into multiple parallel discharge paths using multiple protection transistors. Each transistor provides an independent current path to ground, collectively handling the ESD current burden. This segmented approach distributes the stress on individual devices, allowing smaller geometry transistors to be used while maintaining overall protection capability against ESD events.
Solution Approach 2:
The patent introduces intermediary protection transistors that act as mediators between the ESD voltage source and the sensitive core circuit. These transistors are specifically positioned to intercept ESD currents before they reach the main logic, providing a buffer that protects the smaller-geometry devices in the core circuit from direct ESD exposure while allowing normal signal operation to pass through unaffected.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The voltage clamp effectively limits ESD-induced voltage, reducing the risk of component damage, operates within short ESD event durations, and simplifies circuit design by using standard transistors, thus reducing fabrication costs and complexity.
Implementation Method 1
an electrostatic discharge (ESD) event may expose an electronic circuit to a very high voltage (sometimes thousands of volts) for a relatively short time period
Implementation Method 2
The third transistor may be configured to produce a positive feedback signal based on a first voltage at a gate of the second transistor
Data Source
AI summary
A voltage clamp is disclosed. The voltage clamp may include a plurality of transistors to limit the voltage between a power supply and ground. In addition, the voltage clamp may include a positive feedback signal to reduce turn-on time of the plurality of transistors.