High-Voltage ESD Protection Circuit With Ground-Tracking Gate Clamp
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Solution Overview
Problem
Existing ESD protection circuits fail to effectively reduce voltage across ESD-sensitive circuits during electrostatic discharge events, leading to potential permanent or intermittent failures due to latent defects that are not detected by normal inspection.
Innovation Solution
The proposed ESD protection circuit employs a stack of transistors and an ESD clamp coupled to the gate of a first transistor, enabling a parasitic NPN bipolar transistor in the substrate to discharge current via gate-induced drain leakage, thereby reducing the voltage across the pad and ground by tracking ground voltage, rather than pad voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ESD protection circuits are used, then the circuit structure is simple, but the voltage across ESD-sensitive circuits cannot be effectively reduced during ESD events
Solution Approach 1:
The protection circuit is divided into multiple functional segments: a first transistor (N1) coupled to the pad, a stack of transistors (N3-N5) with intermediate nodes, and an ESD clamp (N6). Each segment performs a specific function in the voltage reduction chain, allowing the complex protection mechanism to be modularly implemented and managed.
Solution Approach 2:
Intermediate nodes (nodes A, B, C between transistors N3-N5) are introduced as mediators to progressively reduce the voltage from the pad. These nodes create staged voltage division, where each transistor in the stack acts as an intermediary element that reduces the voltage burden on subsequent components.
2Productivity
If gate voltage tracks pad voltage, then the transistor operates efficiently during normal conditions, but less current is discharged through the substrate during ESD events
Solution Approach 1:
The gate voltage tracking mechanism is made dynamic through the ESD clamp. During normal operation, the gate voltage tracks the pad voltage for efficient transistor operation. During ESD events, the clamp activates to pull the gate voltage toward ground, dynamically switching the tracking reference based on operating conditions to optimize current discharge.
Solution Approach 2:
The reference voltage for gate tracking changes based on operating conditions. The ESD clamp modifies the gate voltage parameter from tracking pad voltage (high voltage reference) to tracking ground voltage (low voltage reference), thereby changing the electrical parameters to maximize substrate current discharge during ESD events.
3Reliability
If more current is discharged through the substrate, then voltage reduction is improved, but the circuit requires additional components and complexity
Solution Approach 1:
The ESD protection function is merged with the existing transistor structure by utilizing the parasitic NPN bipolar transistor inherent in CMOS technology. The protection mechanism combines the MOSFET stack with the parasitic bipolar action, merging two protective mechanisms into a unified structure that achieves enhanced voltage reduction without requiring completely separate protection circuits.
Solution Approach 2:
The circuit utilizes its own parasitic elements (the inherent NPN bipolar transistor formed by the CMOS structure) to provide protection. Rather than adding entirely external protection components, the design makes the circuit's own parasitic characteristics work in its favor to discharge ESD current through the substrate.
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 reduces the voltage across ESD-sensitive circuits during ESD events, enhancing protection by discharging more current through the substrate, thus preventing catastrophic failures and latent defects.
Implementation Method 1
enabling a parasitic NPN bipolar transistor in the substrate to discharge current via gate-induced drain leakage
Data Source
AI summary
In some aspects of the present disclosure, an electrostatic discharge (ESD) protection circuit is disclosed. In some aspects, the ESD protection circuit includes a first transistor coupled to a pad, a second transistor coupled between the first transistor and ground, a stack of transistors coupled to the first transistor, and an ESD clamp coupled between the stack of transistors and the ground.