HVAC Circuit Trigger String for ESD Protection
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Solution Overview
Problem
Existing high voltage active clamp (HVAC) circuits for protecting electronic circuits from electrostatic discharge (ESD) events face limitations due to parasitic currents and area inefficiency, particularly in high negative voltage applications, where they fail to provide sufficient protection and are not suitable for small IC areas.
Innovation Solution
The implementation of a transient voltage protection circuit using a power MOSFET with a trigger circuit comprising a string of bipolar transistors, substrate diodes, and resistors to control the gate-to-source voltage of the MOSFET, reducing parasitic currents and optimizing area efficiency, allowing protection against both positive and negative overvoltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional HVAC circuits are used for ESD protection, then protection against transient voltage is provided, but parasitic currents increase and area efficiency decreases
Solution Approach 1:
The trigger circuit is divided into multiple trigger elements connected in series, where each element contributes to the overall trigger voltage threshold. This segmentation allows precise control of the trigger point while reducing parasitic current paths, as each segment can be optimized independently for low parasitic current operation.
Solution Approach 2:
Different regions of the circuit are designed with specific properties: the trigger elements use high-impedance configurations to minimize parasitic current, while the discharge path uses low-impedance configurations for effective ESD protection. The substrate diodes are strategically placed to provide localized protection against substrate interference.
2Reliability
If traditional HVAC circuits are used for ESD protection, then protection is provided, but IC area occupied increases
Solution Approach 1:
Multiple functions are merged into a single integrated circuit structure. The trigger circuit, discharge path, and substrate protection mechanisms are combined into one compact HVAC circuit design, reducing the total IC area required compared to separate protection circuits.
Solution Approach 2:
The trigger elements are nested within the overall HVAC circuit structure, with each trigger element containing substrate diodes and resistive elements integrated into its configuration. This nesting allows maximum functional density within minimal area.
3Adaptability or versatility
If trigger voltage threshold is lowered to protect against negative voltage, then protection range increases, but parasitic substrate diode interference increases
Solution Approach 1:
Substrate diodes are introduced as intermediary elements between the trigger circuit and the substrate. These diodes provide a controlled path for substrate currents, preventing unwanted interference while allowing the trigger circuit to operate at lower voltage thresholds for extended protection range.
Solution Approach 2:
The circuit parameters are optimized to change the operating characteristics: resistive elements are selected to provide appropriate biasing, and the trigger element characteristics are adjusted to maintain stability across different protection voltage ranges, preventing parasitic activation.
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 solution effectively limits parasitic effects, maintains high performance, and requires minimal IC area while providing protection beyond -20 V, enhancing the reliability of electronic circuits against ESD events.
Implementation Method 1
each trigger element comprises a bipolar transistor, a substrate diode, and a voltage divider
Implementation Method 2
each trigger element of the first trigger element string comprises a bipolar transistor, a substrate diode, and a voltage divider to divide a voltage across adjacent trigger elements of the first trigger element string
Data Source
AI summary
A transient voltage protection circuit includes a first input/output pad, a second input/output pad, and a trigger circuit coupled between the first input/output pad and the second input/output pad. The trigger circuit includes a first trigger element which includes a first input/output node, a second input/output node, a third input/output node, and a first substrate diode coupled to the third input/output node of the first trigger element. The trigger circuit further includes a first resistor coupled between the first input/output node of the first trigger element and the second input/output node of the first trigger element. The trigger circuit further includes a second trigger element which includes a first input/output node, a second input/output node, a third input/output node, wherein the second input/output node of the first trigger element is coupled to the first input/output node of the second trigger element, and a second substrate diode coupled to the third input/output node of the second trigger element. The trigger circuit further includes a second resistor coupled between the first input/output node of the second trigger element and the second input/output node of the second trigger element.