IGZO Gate Driver Discharge Circuit for Residual Charge Removal
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Solution Overview
Problem
In liquid crystal display devices with monolithic gate drivers, residual charges persist after power shutdown, leading to image retention and display quality issues due to the superior turn-off characteristics of IGZO-TFTs, which cause threshold shifts and operational failures.
Innovation Solution
A display device and method that includes a scanning line drive circuit, a power supply circuit generating distinct scanning line selection potentials, and a discharge unit with a resistor and control switch to sequentially discharge charges from the panel when power is shut off, ensuring quick and stable discharge of residual charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a monolithic gate driver is used in an IGZO-TFT liquid crystal panel, then the device integration and manufacturing are improved, but residual charges persist after power shutdown causing image retention and display quality issues
Solution Approach 1:
The patent applies preliminary action by performing charge discharge operations immediately when power is turned off. The discharge unit is activated to remove residual charges from the pixel capacitance and scanning lines before the next frame is displayed, preventing image retention and display quality degradation. This preliminary discharge action resolves the contradiction by maintaining display quality while preserving the integrated monolithic gate driver structure.
2Reliability
If all scanning lines are selected and black voltage is applied to discharge charges when power is turned off, then residual charges are eliminated, but the discharge process is complex and time-consuming
Solution Approach 1:
The patent extracts the charge discharge function from the main gate driver operation by introducing a separate discharge unit with dedicated discharge resistors. This extracted discharge mechanism operates independently and simplifies the overall discharge process, eliminating the need for complex sequential scanning line selection and black voltage application while ensuring complete charge removal.
Solution Approach 2:
The discharge unit acts as an intermediary between the power supply and the pixel capacitance, providing a dedicated discharge path through discharge resistors. This intermediary mechanism simplifies the discharge process by directly connecting the pixel capacitance to ground without requiring complex scanning line control sequences, thereby reducing device complexity while maintaining discharge effectiveness.
3Reliability
If a discharge unit is added to remove residual charges, then display quality is improved, but power consumption increases during normal operation
Solution Approach 1:
The discharge unit operates periodically rather than continuously, being activated only when power is turned off or when residual charges need to be removed. During normal operation, the discharge resistors remain disconnected or non-conductive, minimizing power consumption. This periodic operation mode resolves the contradiction by maintaining display quality improvement while keeping power consumption low during active usage.
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 removes residual charges from the display panel quickly and stably upon power shutdown, preventing threshold shifts and operational failures, and reduces power consumption during normal operation.
Implementation Method 1
a discharge unit (190) having one terminal connected to the wire (OL), and another terminal grounded; wherein the scanning line drive circuit includes a shift register which has a plurality of bistable circuits corresponding to the scanning lines and sequentially outputs a pulse based on a clock signal
Data Source
AI summary
A gate driver (24) which is provided by an IGZO-GDM and a level shifter circuit (13) are connected to each other via a first through a fifth wires (OL1 through OL5). Each wire (OL) is connected to a discharge unit (190). If an electric power supply to a first through a fifth output circuits (OC1 through OC5) in the level shifter circuit (13) becomes lower than a lower operation limit value during a power-off sequence which is supposed to remove a residual charge from inside a panel, outputs from the first through the fifth output circuits (OC1 through OC5) assume a high-impedance state, whereupon a potential on each wire (OL) is drawn by a discharge unit (190) into a ground potential. Therefore, residual charge inside the panel is removed quickly and stably when power supply is shut off.