MOS Current Source Circuit for Display ESD Protection
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Solution Overview
Problem
Conventional LED driver circuits are vulnerable to static electricity, leading to damage of transistors due to the lack of effective static electricity protection, especially at connection points and within internal circuits.
Innovation Solution
A current source device incorporating a sourcing circuit with high-voltage and low-voltage MOS transistors, a control circuit with an amplifier and resistors, and a discharge circuit to manage and discharge static electricity, utilizing a switching mechanism to protect internal circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LED driver circuit is used without static electricity protection, then the circuit structure is simple and power consumption is low, but the transistor is destroyed by static electricity
Solution Approach 1:
The circuit is divided into two distinct transistor stages: a first MOS transistor (high-voltage type) dedicated to static electricity discharge and a second MOS transistor (low-voltage type) for normal current control. This segmentation allows each component to be optimized for its specific function, with the high-voltage transistor handling electrostatic threats while the low-voltage transistor maintains precise current regulation, thereby improving reliability without excessively complicating the overall circuit.
Solution Approach 2:
The first MOS transistor acts as an intermediary protective element between the external pad and the internal second MOS transistor. When static electricity enters through the pad, the first transistor provides a controlled discharge path to ground, preventing the high-voltage surge from reaching and destroying the second transistor. This intermediary structure protects the sensitive internal circuit while maintaining simplicity.
2Reliability
If high-voltage discharge elements are used to protect against static electricity, then reliability improves, but chip size increases
Solution Approach 1:
The patent utilizes parameter changes by selecting a first MOS transistor with high-voltage breakdown characteristics specifically optimized for electrostatic discharge. By changing the voltage parameter specification of the transistor (using high-voltage type for protection vs. low-voltage type for normal operation), the circuit gains static electricity protection capability without requiring additional specialized high-voltage discharge components that would occupy extra chip area.
3Reliability
If high-voltage discharge elements are used to protect against static electricity, then reliability improves, but power consumption increases
Solution Approach 1:
The protection mechanism operates dynamically: the first MOS transistor remains in a high-impedance state during normal operation, consuming negligible power, and only activates when static electricity is detected at the pad. The transistor's channel conductivity changes dynamically in response to voltage conditions, providing protection only when needed. This dynamic behavior eliminates continuous power consumption associated with static protection 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
Effectively protects internal circuits from static electricity without high-voltage discharge elements, reducing chip size and power consumption while providing stable discharge paths.
Implementation Method 1
a first MOS transistor configured to transmit a current flowing from a pad to a first node in response to a current control voltage
Implementation Method 2
a second MOS transistor configured to transmit the current flowing from the first node to a ground in response to a bias voltage
Implementation Method 3
an amplifier configured to generate the current control voltage based on a setting voltage applied from an outside and a voltage of the first node
Data Source
AI summary
A current source device for electrostatic discharge and a display device including the same are disclosed. The current source device includes a sourcing circuit including a first MOS transistor configured to transmit a current flowing from a pad to a first node in response to a current control voltage, and a second MOS transistor configured to transmit the current flowing from the first node to a ground in response to a bias voltage, and a control circuit including an amplifier configured to generate the current control voltage based on a setting voltage applied from an outside and a voltage of the first node, a first resistor disposed between an output terminal of the amplifier and a gate terminal of the first MOS transistor, and a first switch configured to transmit the bias voltage to a gate terminal of the second MOS transistor in response to a switching control signal.