ESD Protection Circuit With Segmented Isolation Tanks
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Solution Overview
Problem
Conventional ESD protection circuits in integrated circuits are vulnerable to parasitic NPN transistors forming during ESD stress events, which can disrupt the trigger voltage of active shunt transistors, leading to ineffective clamping of ESD current between I/O and ground pads, especially when the deep n-well is connected to multiple pads.
Innovation Solution
The ESD protection circuit incorporates two pull-down transistors in separate isolation tanks, with a boot capacitor driving the gate of the triggering transistor HIGH during ESD events, maintaining a stable trigger voltage for the active shunt transistor by preventing easy charging of parasitic NPN transistors, ensuring continuous current shunting between I/O and ground pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the deep n-well is connected to multiple pads to reduce isolation complexity, then device complexity is reduced, but parasitic NPN transistors form during ESD events disrupting trigger voltage stability
Solution Approach 1:
The isolation deep n-well is segmented into multiple isolated tanks, with each tank containing specific transistors. This segmentation prevents parasitic NPN transistor formation between different tanks while maintaining overall circuit functionality. The first pull-down transistor is in a first isolated tank while other transistors are in a second isolated tank, electrically isolating them during ESD events.
Solution Approach 2:
The boot capacitor acts as an intermediary element that maintains the trigger voltage at the gate of the active shunt transistor during ESD events. It charges during normal operation and discharges during ESD to keep the trigger voltage stable, preventing premature activation of the shunt transistor while ensuring reliable protection when needed.
2Device complexity
If a single large MOSFET is used for ESD protection to simplify circuit design, then device complexity is reduced, but the MOSFET occupies 60% or more of total area of the ESD protection circuit
Solution Approach 1:
The ESD protection function is segmented into multiple smaller transistors (active shunt transistor, first pull-down transistor, second pull-down transistor) distributed across isolated tanks. This segmentation replaces the need for a single large MOSFET, reducing total area occupation while maintaining ESD protection capability through coordinated operation of the segmented components.
Solution Approach 2:
Multiple transistors performing different functions (shunting, pull-down, triggering) are merged into a coordinated ESD protection system. The active shunt transistor, pull-down transistors, and boot capacitor work together as an integrated system, achieving effective ESD protection with smaller individual components compared to a single large MOSFET.
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 configuration effectively maintains a low trigger voltage for the active shunt transistor during ESD events, ensuring reliable ESD current shunting and protection even when the deep n-well is connected to multiple pads, thereby preventing damage to internal IC elements.
Implementation Method 1
with a boot capacitor driving the gate of the triggering transistor HIGH during ESD events, maintaining a stable trigger voltage for the active shunt transistor
Implementation Method 2
An active clamp circuit may include a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) coupled between the I/O and ground pad. This MOSFET is relatively large and often occupies 60% or more of total area of the ESD protection circuit.
Data Source
AI summary
An electrostatic discharge (ESD) protection circuit includes an active shunt transistor, a first pull-down transistor, and a second pull-down transistor. The active shunt transistor is coupled between a first I/O pad and a reference voltage. The first pull-down transistor is connected to the reference voltage. The second pull-down transistor is connected to the first pull-down transistor and the first I/O pad. The first pull-down transistor and the second pull-down transistor are in separate isolation tanks of an isolation deep n-well.