Pixel Circuit Schmitt Trigger for PWM Light-Emitting Time Control
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Solution Overview
Problem
Existing pixel circuits using pulse width modulation (PWM) driving methods face challenges in accurately controlling light-emitting time due to high-frequency signal requirements and differences in transistor threshold voltages, leading to difficulties in achieving uniform display and precise grayscale control.
Innovation Solution
The proposed pixel circuit incorporates a pulse width driving module with a Schmitt trigger, an electrical potential modulation unit, and a display time control unit. This configuration allows for more precise control of the light-emitting time by quickly turning on and off the driving transistor, and it simplifies the circuit structure by eliminating the need for complex threshold voltage compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM driving method is used to achieve high luminous efficiency and constant current, then light-emitting efficiency is improved, but control accuracy of light-emitting time deteriorates due to slow transistor switching
Solution Approach 1:
The circuit performs preliminary voltage preparation in the preparation stage by charging capacitor C1 through transistor T1 with data signal and ELVDD voltage. This preliminary action ensures that when the light-emitting stage begins, all voltage conditions are already prepared, enabling instantaneous transistor switching and precise light-emitting time control without gradual transitions.
Solution Approach 2:
The pixel circuit operates in distinct periodic stages: preparation stage (S1, S3) where voltages are prepared, and light-emitting stage (S2, S4) where light is emitted. This periodic action with clear stage separation ensures that during the light-emitting stage, all transistors switch instantaneously based on pre-prepared voltages, achieving both high efficiency and precise timing control.
2Manufacturing precision
If high-frequency signal SPWM is used to control display time, then light-emitting time control is improved, but gate driver IC complexity and frequency requirements increase
Solution Approach 1:
The circuit prepares all necessary voltages in advance during the preparation stage: capacitor C1 is charged to (ELVDD-Vth1) through transistor T1 with data signal, capacitor C2 is charged to ELVDD through transistor T3, and transistor T4 is prepared with ELVDD at its source electrode. This preliminary voltage preparation eliminates the need for high-frequency gate driver IC signals, achieving precise display time control through pre-configured voltage conditions that enable instantaneous switching.
3Stability of the object's composition
If transistor threshold voltage differences are compensated to achieve uniform display, then display uniformity is improved, but circuit structure complexity increases
Solution Approach 1:
The patent applies local quality by giving each transistor specific voltage conditions tailored to its function: transistor T1 receives data signal at gate, transistor T2 receives boosted voltage at gate, transistor T3 receives ELVDD at gate, and transistor T4 receives ELVDD at source electrode. These localized voltage assignments compensate for threshold voltage differences individually, achieving display uniformity without requiring complex global compensation circuits.
Data Source
AI summary
A pixel circuit and a display panel are provided. The pixel circuit includes a driving transistor T2 and a pulse width driving module. The pulse width driving module includes a display time control unit, an electrical potential modulation unit, and a Schmitt trigger. By connecting the Schmitt trigger in series between an output terminal of the electrical potential modulation unit and a control terminal of the display time control unit, the driving transistor T2 can be turned off more quickly, thereby accurately controlling the display time or light-emitting time of the pixel circuit.