Shift Register Leakage Current Prevention via Dual-Voltage Reset
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Solution Overview
Problem
Conventional shift registers in flat panel display devices experience leakage current issues due to unstable threshold voltages in N-type TFTs, leading to distorted scan pulse outputs and operational failures.
Innovation Solution
A shift register design incorporating a set unit, inverter, output unit, reset unit, and noise cleaner to manage node voltages and prevent leakage current, with specific voltage conditions ensuring transistors are completely turned off, even when threshold voltages shift negatively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If N-type TFTs are used in conventional shift registers, then the circuit can operate with simple structure, but leakage current increases when threshold voltage shifts to negative values
Solution Approach 1:
The patent introduces a dual-voltage reset mechanism where the reset switching element applies different voltages (first reset voltage when turned on, second reset voltage when turned off) to the Q node. This parameter change ensures that even when threshold voltage shifts to negative values, the transistor can be completely turned off by applying a second reset voltage that is lower than the first reset voltage, thereby preventing leakage current while maintaining simple circuit structure
Solution Approach 2:
The noise cleaner unit performs preliminary resetting of the Q node before the main reset operation. By preemptively adjusting the Q node voltage to an appropriate level, the system ensures that subsequent reset operations can effectively completely turn off the transistor even under negative threshold voltage conditions, preventing leakage current before it occurs
2Manufacturing precision
If oxide transistors sensitive to light are used, then manufacturing precision can be improved, but threshold voltage shifts to negative values due to light exposure
Solution Approach 1:
The patent applies preliminary anti-action by using the noise cleaner to preemptively counteract the threshold voltage shift caused by light exposure. The noise cleaner resets the Q node to an appropriate voltage level before the light-induced threshold shift can cause instability, thereby maintaining stable operation despite using light-sensitive oxide transistors with improved manufacturing precision
Solution Approach 2:
The dual-voltage reset mechanism provides feedback-based stabilization. The reset switching element monitors the Q node state and applies appropriate reset voltages (first or second reset voltage) based on the operational conditions, ensuring that threshold voltage shifts due to light exposure are compensated and stability is maintained
3Ease of operation
If gate voltage is applied to turn off transistors, then logical off state is achieved, but leakage current flows because Vgs > 0V
Solution Approach 1:
The patent fundamentally changes the voltage parameter applied to the transistor gate. Instead of using conventional gate voltages where Vgs > 0V, the reset switching element applies a second reset voltage that is lower than the first reset voltage, ensuring Vgs becomes sufficiently negative to completely turn off the transistor and eliminate leakage current, while maintaining ease of operation through automated voltage switching
Data Source
AI summary
A shift register capable of preventing leakage current and a display device using the same are disclosed. The shift register includes a plurality of stages. Each stage includes a set unit setting a Q node in response to a start pulse or previous output, an inverter for controlling a QB node to have a logic state opposite to that of the Q node, an output unit for outputting any one input clock or a gate off voltage in response to the logic states of the Q and QB nodes, a reset unit including a reset switching element, the reset switching element resetting the Q node with a first reset voltage in response to a reset pulse or next output, and a noise cleaner resetting the Q node with a second reset voltage in response to the QB node. When the reset switching element is turned off, the first reset voltage is greater than a voltage of the reset pulse or the next output for the current.