PMOS ESD Protection Circuit for CDM Event Prevention
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Solution Overview
Problem
Integrated circuits (ICs) are susceptible to damage from Charged-Device Model (CDM) electrostatic discharge (ESD) events due to rapid and high current discharges, which can occur before traditional ESD protection circuits are activated, leading to potential internal circuit damage.
Innovation Solution
The implementation of an ESD protection circuit utilizing a P channel metal oxide semiconductor (PMOS) transistor and a resistor coupled between the PMOS transistor's gate and power rail, enabling an initial-on mechanism that enhances turn-on speed and provides efficient CDM ESD protection by immediately conducting ESD current to ground when a pin is grounded.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional ESD protection circuits are used, then they can protect against HBM and MM ESD events, but they cannot activate fast enough to protect against CDM ESD events which occur in less than 2 nanoseconds
Solution Approach 1:
The PMOS transistor is pre-biased through the impedance device to be in a partially conductive state before ESD event occurs. This preliminary action allows the transistor to switch on much faster when CDM ESD strikes, since it doesn't need to go through full turn-on delay. The gate is pre-charged through the impedance device, so when discharge occurs, the transistor immediately begins conducting to shunt the ESD current away from sensitive circuits.
2Reliability
If the ESD protection circuit is designed to activate quickly, then it can protect against CDM ESD events, but the circuit complexity increases due to additional PMOS transistor and impedance device
Solution Approach 1:
The ESD protection function is merged with the existing input stage circuitry. The PMOS transistor's source connects to the NMOS gate, and its drain connects to the NMOS source/ground, integrating the protection path into the signal path. The impedance device is merged with existing biasing or pull-up networks. This merging approach adds protection functionality without requiring completely separate protection circuit blocks, thereby limiting the increase in overall circuit complexity.
Solution Approach 2:
The PMOS transistor serves multiple functions: it acts as the main ESD protection switch for CDM events, provides a discharge path for substrate charge, and can work in conjunction with existing clamp circuits for HBM/MM protection. The impedance device serves both as a gate biasing element and as part of the ESD protection network. This multi-functionality reduces the need for dedicated separate components for each protection mode.
3Speed
If the PMOS transistor gate is directly connected to power rail, then the circuit is simpler, but the turn-on speed is insufficient for CDM ESD protection
Solution Approach 1:
The gate voltage parameter of the PMOS transistor is dynamically changed through the impedance device. During normal operation, the impedance device charges the gate to a specific voltage level that keeps the transistor in a pre-biased state. During CDM ESD, the gate voltage rapidly changes as the transistor turns on, allowing the gate to discharge through the low-impedance path created by the transistor's channel. This parameter change approach enables fast switching without complex active control circuits.
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 proposed solution effectively prevents CDM ESD-induced damage to internal circuits by ensuring rapid activation and efficient current dissipation, thereby protecting nanoscale CMOS process input stages from CDM ESD events.
Implementation Method 1
the electrostatic charge originally stored within the IC will be discharged through the grounded pin. This is called the CDM ESD event. The CDM ESD event delivers a large amount of current in a very short period of time
Implementation Method 2
an impedance device (for example, a resistor), wherein the PMOS transistor has a source coupled to a gate of the first NMOS transistor, and a drain coupled to a source of the first NMOS transistor, and the impedance device is coupled between a gate of the PMOS transistor and a first power rail
Data Source
AI summary
An electrostatic discharge (ESD) protection circuit, suitable for an input stage circuit including a first N channel metal oxide semiconductor (NMOS) transistor, is provided. The ESD protection circuit includes an P channel metal oxide semiconductor (PMOS) transistor and an impedance device, in which the PMOS transistor has a source coupled to a gate of the first NMOS transistor, and a drain coupled to a source of the first NMOS transistor, and the impedance device is coupled between a gate of the PMOS transistor and a first power rail to perform a initial-on ESD protection circuit. The ESD protection circuit formed by the PMOS transistor and the resistor is capable of increasing the turn-on speed of the ESD protection circuit and preventing the input stage circuit from a CDM ESD event.