Scan Signal Slew Rate Circuit for Hot-Carrier Stress Control
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Solution Overview
Problem
Active-matrix devices with large storage capacitors and transistors experience drain avalanche hot-carrier stress and signal distortion due to rapid scan signal changes, leading to non-uniform operation and reduced reliability.
Innovation Solution
Incorporation of a slew rate control circuit with transistors configured to adjust the scan signal's rise and fall times, using transistors that form diodes or source follower amplifiers to mitigate hot-carrier stress and signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If large storage capacitors and large transistors are used in pixel circuits, then control voltage drop is mitigated and fast scanning operations are achieved, but drain avalanche hot-carrier stress and large kickback effect occur in the scan transistor
Solution Approach 1:
The patent introduces a scan transistor protection circuit as an intermediary component between the scan driver and the scan transistor. This protection circuit includes a first transistor connected in parallel with the scan transistor, where the first transistor has a larger threshold voltage. The protection circuit acts as a mediator that prevents direct exposure of the scan transistor to extreme voltage conditions, thereby reducing hot-carrier stress and kickback effects while maintaining fast scanning operations.
2Stress or pressure
If large scan transistors are used, then control voltage drop is reduced, but input impedance becomes small causing scan signal distortion and slowing down rise and fall speed
Solution Approach 1:
The scan transistor protection circuit serves as an intermediary that buffers the scan signal before it reaches the large scan transistor. The first transistor in the protection circuit, with its larger threshold voltage, prevents direct coupling of the scan driver output to the scan transistor gate, thereby reducing signal distortion while maintaining adequate voltage control.
Solution Approach 2:
The patent utilizes transistors with different threshold voltage parameters. The first transistor in the protection circuit is designed with a larger threshold voltage compared to the scan transistor, creating a parameter difference that enables the protection function. This parameter change allows the system to maintain both low voltage drop and reduced signal distortion.
3Productivity
If rapid rise and fall of scan signal is implemented, then fast scan operation is achieved, but drain avalanche hot-carrier stress and large kickback effect are caused
Solution Approach 1:
The protection circuit acts as a buffer between the fast-switching scan driver and the scan transistor. The first transistor with larger threshold voltage slows down the voltage transition at the scan transistor gate, reducing the rate of change (dV/dt) that causes hot-carrier stress and kickback effects, while still allowing fast scan operations to proceed.
Solution Approach 2:
The scan transistor protection circuit provides beforehand cushioning by pre-conditioning the scan signal before it reaches the vulnerable scan transistor. The parallel connection of the first transistor creates a protective pathway that cushions the scan transistor against harmful voltage transients and rapid changes, preventing hot-carrier stress before it occurs.
Data Source
AI summary
An electronic device is provided. The electronic device includes a slew rate control circuit. The slew rate control circuit includes a first transistor, a second transistor, an input terminal, and an output terminal. The slew rate control circuit is configured to receive a scan signal switching between a first high voltage level and a first low voltage level, and output an adjusted scan signal switching between a second high voltage level and a second low voltage level. The first transistor and the second transistor are the same type of transistors, and each forms a diode or a source follower amplifier.