Unit Shift Register Circuit Bi-Directional Precharge Stability
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Solution Overview
Problem
The existing unit shift register circuits face issues with characteristics degradation due to threshold voltage fluctuations in oxide semiconductor TFTs, leading to unstable precharge voltages and increased circuit complexity for bi-directional shift operations.
Innovation Solution
A unit shift register circuit configuration with specific transistor arrangements and input signal timing, where the second and third transistors serve as set and reset transistors in forward and backward operations respectively, using input signals with varying voltages to maintain stable precharge voltages without diode connections, reducing the number of circuit elements required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode-connected set TFT is used to precharge the gate electrode of the output TFT, then the precharge function is achieved, but the precharge voltage decreases by the threshold voltage of the TFT and characteristics degradation progresses over time
Solution Approach 1:
The patent extracts the diode connection constraint from the set TFT, allowing the TFT to function as a set transistor without the voltage loss inherent in diode connections. This separates the precharge function from the voltage penalty, enabling stable precharge voltage while maintaining circuit simplicity.
Solution Approach 2:
The patent changes the operating parameters of the set TFT by controlling its gate electrode potential independently from the drain-source path. By applying specific gate voltages (Vgg1, Vgg2) that are higher than the threshold voltage, the set TFT can maintain stable precharge voltage without the voltage drop characteristic of diode-connected configurations.
2Ease of manufacture
If oxide semiconductor TFTs are used in the shift register circuit, then the circuit can be fabricated with monolithic circuit technology, but threshold voltage fluctuates due to voltage stress and characteristics degradation progresses
Solution Approach 1:
The patent applies preliminary action by pre-charging the gate electrode of the output TFT to a voltage higher than the threshold voltage before the switching operation. This preliminary precharge compensates for the threshold voltage fluctuation that occurs during operation, ensuring stable circuit performance over time despite oxide semiconductor characteristics.
Solution Approach 2:
The patent implements a feedback mechanism where the potential of the gate electrode is continuously monitored and adjusted through the set TFT. By controlling the gate voltage based on the actual potential state, the circuit compensates for threshold voltage fluctuations and maintains stable operation.
3Adaptability or versatility
If bi-directional shift operation is implemented, then scanning line driving can switch between forward and backward directions, but the circuit requires additional set and reset TFTs increasing the number of circuit elements
Solution Approach 1:
The patent applies universality by designing the set TFT and reset TFT to perform multiple functions. The same set TFT can precharge the gate electrode during both forward and backward operations, and the reset TFT can discharge the gate electrode in both directions. This multi-functionality reduces the total number of circuit elements required for bi-directional operation.
Solution Approach 2:
The patent merges the set and reset functions into a unified circuit structure where the second and third transistors serve dual purposes. By combining these functions and controlling them through coordinated gate voltage signals, the circuit achieves bi-directional operation without requiring separate dedicated transistors for each direction.
Data Source
AI summary
In a forward shift operation, a second input signal having a higher voltage than a voltage of a first input signal is input to a second gate terminal in a case that a first gate terminal of a first transistor is charged, and a fourth input signal having a higher voltage than a voltage of a third input signal is input to a third gate terminal in a case that the first gate terminal of the first transistor is discharged. In a backward shift operation, the fourth input signal having a higher voltage than a voltage of the third input signal is input to the third gate terminal in a case that the first gate terminal of the first transistor is charged, and the second input signal having a higher voltage than a voltage of the first input signal is input to the second gate terminal in a case that the first gate terminal of the first transistor is discharged.