Bootstrap Clamp Circuit for ESD Protection in Integrated Circuits
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Solution Overview
Problem
Integrated circuits face challenges in protecting input/output transistors from electrostatic discharge (ESD) events, particularly from human body, machine, and charged device models, which can cause damage due to rapid current flows and voltage spikes, and existing solutions often require large protection resistors or added capacitance that degrade performance or increase area.
Innovation Solution
The implementation of a bootstrap clamp circuit that includes a protection resistor between the input/output transistor and bondpad, and a bootstrap clamp transistor or diode between the drain and gate of the input/output transistor, along with optional biasing resistors, to provide effective ESD protection with reduced series resistance and area occupancy, allowing for flexible design and protection against both positive and negative polarity discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protection resistor is used to protect the input/output transistor from ESD events, then the transistor is protected from damage, but the series resistance increases which degrades performance
Solution Approach 1:
The bootstrap clamp circuit is pre-configured with the protection resistor in series with the clamp device. During normal operation, the clamp device remains off and the protection resistor has minimal impact. When an ESD event occurs, the clamp device turns on rapidly, and the same protection resistor now serves to limit the ESD current while the clamp provides the low-impedance path to ground. This preliminary configuration allows the resistor to serve dual purposes without significant performance degradation during normal operation.
Solution Approach 2:
The invention changes the operational state of the clamp device from always-on to dynamically controlled. By using the bootstrap capacitor to raise the gate voltage above the drain voltage during ESD events, the clamp device transitions from a high-resistance state (off during normal operation) to a low-resistance state (on during ESD). This parameter change allows the protection resistor to have minimal effect during normal operation while providing adequate current limiting during ESD protection.
2Reliability
If a bootstrap clamp circuit is added to protect against ESD events, then ESD protection is improved, but the area occupancy increases
Solution Approach 1:
The bootstrap clamp circuit merges multiple functions into a single integrated structure. The protection resistor serves both as a current limiter during ESD events and as part of the biasing network for the clamp device. The bootstrap capacitor is formed using the existing gate-drain capacitance of the clamp device itself, eliminating the need for a separate dedicated capacitor. This merging of functions reduces the overall area required compared to traditional ESD protection circuits that use separate components for each function.
Solution Approach 2:
The clamp device serves multiple functions: it acts as the ESD protection switch, provides the low-impedance path to ground during ESD events, and its inherent gate-drain capacitance serves as the bootstrap capacitor. The protection resistor also serves dual purposes as both current limiting element and biasing component. This multi-functionality reduces the number of discrete components needed and thereby reduces area occupancy.
3Reliability
If a large protection resistor is used to limit ESD current, then the transistor is protected from excessive current, but the voltage drop across the resistor increases which degrades signal integrity
Solution Approach 1:
The bootstrap capacitor is pre-charged during normal operation to a voltage slightly higher than the drain voltage. When an ESD event occurs, this pre-charged capacitor rapidly raises the gate voltage above the drain voltage, causing the clamp device to turn on quickly. This preliminary charging action ensures that the clamp responds rapidly to ESD events, minimizing the duration during which the protection resistor causes voltage drop and signal degradation.
Solution Approach 2:
The clamp device transitions from a static off-state during normal operation to a dynamic on-state during ESD events. The bootstrap mechanism dynamically adjusts the gate voltage based on the drain voltage, ensuring that the clamp only activates when needed. This dynamic behavior allows the protection resistor to have minimal impact during normal operation while providing adequate current limiting during ESD protection, thereby reducing voltage drop and signal integrity degradation.
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
This solution effectively protects integrated circuits from ESD events by reducing the required series resistance and area, maintaining performance while ensuring the transistor turns on during ESD events to prevent damage, and allows for a single design to be used across various driver output resistances.
Implementation Method 1
Electrostatic discharge (ESD) is a continuing problem in the design, manufacture, and utilization of integrated circuits (ICs).
Data Source
AI summary
An integrated circuit with a boot strap clamp protecting an input/output transistor coupled to a bondpad where the boot strap clamp is comprised of a protection resistor coupled between the input/output transistor and the bondpad and a bootstrap clamp transistor coupled between the drain of the input/output transistor and the gate of the input/output transistor. An integrated circuit with a boot strap clamp protecting an input/output transistor coupled to a bondpad where the boot strap clamp is comprised of a protection resistor coupled between the input/output transistor and the bondpad and a bootstrap clamp diode coupled between the drain of the input/output transistor and the gate of the input/output transistor and a biasing resistor coupled between the gate and source of the input/output transistor.