ESD Protection Circuit Gate Voltage Control for NMOS Transistors
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Solution Overview
Problem
In semiconductor processing, ESD events can turn on LDNMOS transistors, causing direct damage due to non-zero gate voltage, and existing ESD protection circuits with lower trigger-on voltages are insufficient to protect these transistors.
Innovation Solution
An ESD protection circuit that grounds the gate of an NMOS transistor using a gate voltage control device, comprising a discharge NMOS transistor, PMOS transistors, and NMOS transistors, ensuring the NMOS transistor is turned off during an ESD event by utilizing a connection node and parasitic diodes to manage ESD voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PNP or NPN bipolar transistor is used as an ESD protection device with a trigger-on voltage lower than the breakdown voltage of the protected device, then the layout area is efficiently utilized and the trigger-on voltage is reduced, but the protected device cannot be protected when ESD voltage is present at its gate because the device turns on and ESD current passes through it
Solution Approach 1:
The patent introduces a gate voltage control device as an intermediary between the ESD protection circuit and the gate of the NMOS transistor. This control device actively manages the gate voltage to ensure it remains at 0V during ESD events, preventing the NMOS transistor from turning on. The intermediary component decouples the protection mechanism from the transistor gate, allowing independent control of the gate voltage regardless of ESD conditions.
Solution Approach 2:
The patent applies preliminary anti-action by proactively grounding the gate of the NMOS transistor before ESD current can flow through it. The gate voltage control device is designed to detect ESD events and immediately counteract any voltage rise at the gate by providing a low-impedance path to ground, preventing the harmful effect of gate voltage before it can occur.
2Device complexity
If the gate of the NMOS transistor is not actively controlled, then the circuit structure is simpler, but the NMOS transistor turns on during ESD events causing direct damage
Solution Approach 1:
The gate voltage control device serves as an intermediary that adds minimal complexity while maximizing protection effectiveness. It consists of control transistors and associated circuitry that actively monitor and control the gate voltage, acting as a buffer between the ESD event and the NMOS transistor gate.
Solution Approach 2:
The patent implements feedback mechanisms where the state of the NMOS transistor and the ESD protection circuit is continuously monitored, and the gate voltage control device adjusts the gate voltage accordingly. When ESD events are detected, the feedback loop triggers the control device to ground the gate, ensuring the transistor remains off.
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
Effectively prevents ESD current from passing through the NMOS transistor by ensuring it remains off during an ESD event, thereby protecting it from damage.
Implementation Method 1
an ESD protection circuit to ground the gate of a subject NMOS transistor via a gate voltage control device to ensure that the NMOS transistor is turned off in an ESD event
Data Source
AI summary
An ESD protection circuit, which protects a subject NMOS transistor coupled between an I/O pad and a ground, includes a first discharge device arranged between the I/O pad and the ground, having a trigger-on voltage that is lower than a breakdown voltage of the subject NMOS transistor; and a gate voltage control device, including a discharge NMOS transistor coupled to the ground and a gate of the subject NMOS transistor; a first PMOS transistor connected to the gate of the subject NMOS transistor and a connection node; and a first NMOS transistor connected to the connection node and the ground. The connection node is connected to the gate of the discharge NMOS transistor, and the gate of the first PMOS transistor and the gate of the first NMOS transistor are connected to each other.