Display Driver Precharge Circuit for Transistor Voltage Protection
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Solution Overview
Problem
In liquid crystal display panels, the existing display drivers face challenges in maintaining a reduced circuit size without shortening the service life of transistors due to voltage exceeding their withstand voltage during polarity switching, leading to potential degradation of the liquid crystal material.
Innovation Solution
A display driver with a precharge circuit that precharges output nodes to an intermediate voltage before polarity switching, ensuring that the voltage applied to transistors does not exceed their withstand voltage, thus preventing transistor degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the maximum voltage VDD is applied to decoders to reduce circuit size, then the transistor size can be minimized, but the voltage exceeds the withstand voltage of transistors during polarity switching, shortening service life
Solution Approach 1:
The precharge circuit performs preliminary action by precharging the output nodes to the intermediate voltage VDD/2 before polarity switching occurs. This preparatory step ensures that when the switch circuit reverses the polarity, the voltage difference across transistors remains within the withstand voltage limit, preventing damage while maintaining the compact circuit design with VDD/2 transistor rating.
2Area of moving object
If transistors with withstand voltage VDD/2 are used to reduce circuit size, then area is minimized, but voltage exceeding VDD/2 during polarity switching causes transistor degradation
Solution Approach 1:
The precharge circuit provides beforehand cushioning by maintaining the output nodes at the intermediate voltage VDD/2 before polarity switching. This cushioning effect absorbs the voltage stress that would otherwise exceed the VDD/2 withstand voltage of the transistors, protecting them from degradation while enabling the use of smaller, more area-efficient transistors rated for VDD/2.
3Speed
If polarity switching is performed without precharging, then circuit operation speed is maintained, but voltage spikes exceed transistor withstand voltage, reducing reliability
Solution Approach 1:
The precharge circuit executes preliminary action by precharging output nodes to VDD/2 before the polarity switching operation. This preliminary step prevents voltage spikes during switching that would exceed transistor withstand voltage, ensuring reliable operation while maintaining fast switching speeds through the efficient use of the switch circuit and precharge circuit configuration.
Data Source
AI summary
A display driver according to the present invention includes a withstand voltage protection part that precharges an output node of a polarity changeover switch circuit that switches a polarity of a drive signal supplied to a display device from an electric potential of a positive polarity (a first electric potential to a third electric potential) to an electric potential of a negative polarity (the third electric potential to a second electric potential) or vice versa to the third electric potential immediately before the polarity switching.