Gate Driving Circuit Back Bias Control for Threshold Stability
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Solution Overview
Problem
The reliability of gate driving circuits in display apparatuses is compromised due to shifts in transistor threshold voltages, particularly when operated for extended periods at high temperatures, leading to increased leakage currents and reduced circuit performance.
Innovation Solution
Incorporating a signal controller that senses current variations in the gate-on voltage and outputs a back bias control voltage to adjust the threshold voltage of four-terminal transistors within the gate driving circuit, ensuring the threshold voltage is maintained at a desired level, thereby enhancing the reliability of the gate driving circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the gate driving circuit is operated for extended periods at high temperatures, then the circuit can maintain continuous operation, but the transistor threshold voltage shifts leading to increased leakage currents and reduced reliability
Solution Approach 1:
The patent implements a feedback mechanism where the current through the voltage output terminal is continuously sensed by a signal controller. Based on the sensed current variation, the controller dynamically adjusts the back bias control voltage applied to the four-terminal transistors. This feedback loop compensates for threshold voltage shifts caused by high-temperature operation, maintaining circuit reliability during extended continuous operation.
Solution Approach 2:
The patent changes the electrical parameter (back bias control voltage) of the four-terminal transistors to compensate for threshold voltage shifts. By dynamically adjusting the back bias voltage based on sensed current variations, the system modifies the transistor operating parameters to maintain desired threshold voltage levels, thereby improving reliability under extended operation conditions.
2Device complexity
If conventional transistors are used in the gate driving circuit, then the device complexity is low, but the threshold voltage cannot be dynamically adjusted to compensate for leakage currents
Solution Approach 1:
The patent introduces asymmetry by using four-terminal transistors instead of conventional three-terminal transistors. The additional terminal (back bias terminal) allows independent control of the threshold voltage, creating an asymmetric structure that enables dynamic threshold adjustment. This asymmetric design provides the extra degree of freedom needed to compensate for leakage currents while maintaining reasonable device complexity.
3Ease of operation
If the threshold voltage of transistors is not adjusted, then the circuit operation is simple, but leakage currents increase during extended operation reducing performance
Solution Approach 1:
The patent implements a self-service mechanism where the gate driving circuit automatically monitors and corrects its own threshold voltage drift. The signal controller senses current variations and automatically adjusts the back bias control voltage without external intervention. This self-service approach maintains circuit performance during extended operation while adding minimal operational complexity, as the adjustment occurs automatically based on internal sensing.
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
This approach effectively stabilizes the threshold voltage of transistors, reducing leakage currents and improving the long-term reliability and performance of the gate driving circuit by dynamically adjusting the back bias control voltage in response to sensed current variations.
Implementation Method 1
a signal controller configured to sense a variation in current of the voltage output terminal to output a back bias control voltage corresponding to the sensed current variation
Data Source
AI summary
A display apparatus includes: a display panel including a plurality of pixels respectively connected to a plurality of gate lines; a gate driving circuit including a plurality of driving stages configured to apply gate signals to the gate lines; a voltage generator configured to output a gate-on voltage through a voltage output terminal thereof; and a signal controller configured to sense a variation in current of the voltage output terminal to output a back bias control voltage corresponding to the sensed current variation, wherein each of the driving stages comprises a plurality of oxide thin film transistors and at least one of the oxide thin film transistors is a four-terminal transistor in which a threshold voltage thereof is controlled by the back bias control voltage.