Shift Register Circuit Light Shielding Film Selective Application
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Solution Overview
Problem
Conventional shift register circuits in liquid crystal display devices face malfunctions due to threshold voltage shifts in thin-film transistors caused by external light, which can be exacerbated by the use of light shielding films that increase leak current and unwanted capacitance, leading to waveform distortion and operational failures.
Innovation Solution
A shift register circuit design where a light shielding film is selectively applied to specific transistors based on their on-duty cycles, with n-channel and p-channel transistors receiving positive or negative biases, to minimize threshold shifts and prevent malfunctions, while avoiding the need for extensive light shielding that increases capacitance and leak current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light shielding film is provided for all thin-film transistors in the shift register circuit, then threshold voltage shifts due to external light are prevented, but off-leak current increases and waveform distortion occurs
Solution Approach 1:
The patent applies light shielding films selectively only to specific transistors (T1, T2, T3) that are susceptible to threshold voltage shifts, rather than all transistors in the circuit. This localized approach prevents threshold shifts in critical transistors while avoiding the harmful off-leak current effects that would occur if all transistors were shielded.
2Reliability
If a light shielding film is provided for thin-film transistors, then threshold voltage shifts are prevented, but unwanted capacitance increases causing waveform rounding
Solution Approach 1:
The patent limits light shielding film application to only those transistors where threshold voltage stability is critical (T1, T2, T3), thereby minimizing the total unwanted capacitance introduced by light shielding films while still achieving reliable prevention of threshold shifts in the most vulnerable components.
3Reliability
If extensive light shielding is applied to the shift register circuit, then threshold voltage shifts are prevented, but leak current increases and operational failures occur
Solution Approach 1:
The patent implements a selective light shielding strategy applied only to transistors T1, T2, and T3 that are most susceptible to threshold voltage shifts. This localized approach prevents the extensive leak current problems that would result from comprehensive light shielding across the entire shift register circuit.
Data Source
AI summary
Provided is a shift register circuit capable of preventing occurrence of malfunction caused by a threshold shift of a thin-film transistor due to an influence of external light. A unit circuit constituting each stage of the shift register circuit includes a plurality of thin-film transistors. The plurality of thin-film transistors are categorized into a first group (T2, T4, T9) whose on-off state is controlled at relatively high on-duty and a second group (T1, T3, T5, T6, T7, T8) whose on-off state is controlled at relatively low on-duty. In such a configuration, a light shielding film (LS) is provided only for the thin-film transistor included in one of the first group and the second group.