SCR TVS Layout for Low-Capacitance High-Holding-Voltage Protection
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Solution Overview
Problem
Existing transient voltage suppressor (TVS) protection solutions for high-speed applications, such as HDMI connectors, face challenges in achieving low capacitance at protected nodes while maintaining high holding voltage after snap-back, which is essential to prevent interference with data speed and ensure effective protection against over-voltage events.
Innovation Solution
The proposed solution involves a silicon controlled rectifier (SCR) based TVS protection device with alternating emitter and base regions arranged interleaving in a direction orthogonal to the current path. This configuration realizes low capacitance at the protected node in blocking mode and provides a high holding voltage in the conduction mode, ensuring effective surge protection without interfering with high-speed data operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional TVS protection devices are used, then surge protection is provided, but capacitance is high which interferes with high-speed data operations
Solution Approach 1:
The TVS device is segmented into multiple functional regions: a first TVS diode for voltage suppression, a second TVS diode for bidirectional protection, and a steering diode for current direction control. This segmentation allows each component to be optimized for its specific function, achieving low capacitance while maintaining surge protection capability.
Solution Approach 2:
A steering diode is introduced as an intermediary component between the TVS diodes and the protected circuit. This steering diode acts as a mediator that directs current flow during ESD events while presenting low capacitance to the high-speed data line, thus protecting the circuit without interfering with data transmission.
2Speed
If low capacitance TVS devices are used for high-speed data pins, then data speed is maintained, but holding voltage after snap-back is insufficient
Solution Approach 1:
Multiple TVS diodes with different characteristics are combined in a parallel configuration. The first TVS diode provides primary suppression with one holding voltage characteristic, while the second TVS diode provides additional suppression with a higher holding voltage characteristic. This merging allows the device to maintain low capacitance while achieving higher holding voltage through the combined effect of multiple diodes.
Solution Approach 2:
The protection device uses a composite structure combining different types of TVS diodes (unidirectional and bidirectional) with different breakdown voltage characteristics. This composite approach allows the system to exhibit multiple holding voltage levels, ensuring that the overall device maintains both low capacitance and high holding voltage after snap-back.
3Reliability
If high surge protection is provided for power supply pins, then protection capability is enhanced, but capacitance increases which may affect circuit performance
Solution Approach 1:
Different regions of the protection device are assigned different functional qualities: the first TVS diode is optimized for high surge protection capability with appropriate capacitance, while the second TVS diode and steering diode are optimized for low capacitance characteristics. This local quality differentiation allows the overall device to provide high surge protection for power supply pins while maintaining acceptable capacitance levels.
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 SCR based TVS device achieves a low capacitance value of less than 0.2 pF at the protected node while maintaining a high holding voltage above the maximum operating voltage of HDMI coupled devices. This configuration effectively protects high-speed data pins and I/O terminals from over-voltage transient conditions, making it suitable for applications like HDMI 2.1 data ports or connectors.
Implementation Method 1
the SCR includes alternating emitter and base regions arranged interleaving in a direction along a major surface of a semiconductor layer and orthogonal to a current path of the SCR
Implementation Method 2
the power supply pins and the data pins of the electronic devices both require protection from over-voltages conditions due to ESD events or switching and lightning transient events
Implementation Method 3
provides a high holding voltage in the conduction mode, ensuring effective surge protection without interfering with high-speed data operations
Data Source
AI summary
A transient voltage suppressor (TVS) device includes a silicon controlled rectifier (SCR) as the clamp device between a high-side steering diode and a low-side steering diode. The SCR includes alternating emitter and base regions arranged interleaving in a direction along a major surface of a semiconductor layer and orthogonal to a current path of the SCR. The TVS device realizes low capacitance and high holding voltage at the protected node.