Electro-optical Device Threshold Voltage Compensation
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Solution Overview
Problem
Existing techniques for compensating for threshold voltage errors in transistors are ineffective when applied to high resistance electro-optical elements like electrophoresis or liquid crystal elements, as they fail to establish a stable gate-source voltage due to low current flow.
Innovation Solution
A pixel circuit configuration that includes a driving transistor, capacitive elements, and a switch, where the switch is controlled to vary the potential at the control terminal to ensure the driving transistor is turned on, allowing for effective compensation of threshold voltage errors by setting the potential to a compensation initial value and varying the voltage between the control and first terminals over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the driving transistor and switch are controlled to be in a turned-on state during the writing period, then the gate-source voltage should converge to the target voltage Vrst, but the potential at the circuit point is not determined due to low current flow through high resistance electro-optical elements
Solution Approach 1:
The patent applies preliminary action by performing a reset operation before the writing period to establish a determined potential at the circuit point. The reset switch is turned on during a reset period to set the potential at the circuit point to a known state (first potential), ensuring that the potential is determined before the writing period begins. This preliminary setup allows the subsequent writing operation to proceed with reliable potential determination even when current flow through the electro-optical element is minimal.
2Adaptability or versatility
If a high resistance electro-optical element such as an electrophoresis element or liquid crystal element is connected to the circuit point, then the device can display images, but a current hardly flows through the electro-optical element causing the potential at the circuit point to be undetermined
Solution Approach 1:
The patent introduces an intermediary approach by using the reset switch and reset period as a mediator mechanism. The reset switch acts as an intermediary component that temporarily connects the circuit point to a known potential source during the reset period, establishing a determined potential state. This intermediary reset mechanism allows the system to overcome the low current flow problem of high resistance electro-optical elements by externally setting the potential before the main operation begins.
3Measurement precision
If the writing period is extended to ensure compensation, then the grayscale control accuracy improves, but the display response time increases
Solution Approach 1:
The patent applies segmentation by dividing the operation period into distinct segments: a reset period for establishing potential, a writing period for compensation operation, and a driving period for grayscale control. The reset period is separated from the writing period, allowing the compensation operation to be performed efficiently without extending the overall display response time. The driving period follows independently, enabling rapid grayscale control based on the pre-established potential state.
Data Source
AI summary
An electro-optical device includes a pixel circuit, and a driving circuit. The pixel circuit includes a driving transistor, a first capacitive element, an electro-optical element, and a switch. The driving circuit controls the switch to be turned off, varies a potential such that the driving transistor is turned on, during a first period, sets a potential at a control terminal to a compensation initial value by controlling the switch to be turned on, during a second period, supplies a grayscale potential corresponding to a designated grayscale, varies a driving potential such that the driving transistor is turned on, during a third period, and varies a voltage between the control terminal and a first terminal with the passage of time, during a fourth period.