AMOLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
In existing AMOLED display panels, the non-uniformity of TFT switching circuits due to manufacturing limitations affects the uniformity and constancy of luminance, leading to a significant difference between data output from the IC and data written to the pixel circuit, which decreases display quality.
Innovation Solution
A pixel circuit comprising multiple transistors and a storage capacitor is designed to control the switching and charging/discharging of the light-emitting element, reducing the voltage written to the driving transistor in a diode connection manner, making the current flowing through the transistor independent of the threshold voltage and initial voltage, thus avoiding inconsistencies in luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an AMOLED pixel compensation circuit is used to compensate for TFT threshold voltage, then the uniformity of display luminance is improved, but the writing speed decreases and data writing accuracy deteriorates due to large internal resistance in diode-connection state
Solution Approach 1:
The patent dynamically changes the connection state of the driving transistor between diode-connection mode (for compensation) and saturation mode (for data writing). During compensation phase, the transistor is connected in diode configuration to compensate threshold voltage. During data writing phase, the transistor is switched to saturation mode to reduce internal resistance and improve writing accuracy. This dynamic state transition resolves the contradiction between luminance uniformity and data writing accuracy.
Solution Approach 2:
The patent implements periodic switching between compensation operation and data writing operation. The compensation circuit operates during specific time periods to adjust threshold voltage, then the system transitions to data writing period with reduced internal resistance. This periodic alternation allows both luminance uniformity compensation and accurate data writing to be achieved at different time phases.
2Reliability
If the driving transistor is in diode-connection state during compensation, then threshold voltage compensation is achieved, but the internal resistance increases causing slower writing speed
Solution Approach 1:
The patent dynamically transitions the driving transistor between diode-connection state (for compensation) and saturation state (for fast writing). During compensation phase, diode connection provides reliable threshold voltage compensation. During data writing phase, the transistor switches to saturation mode where internal resistance is significantly reduced, enabling faster writing speed. This dynamic state change resolves the speed-reliability contradiction.
3Reliability
If high potential is applied to the gate during compensation (Vdata+Vth or Vdd+Vth), then threshold voltage compensation is achieved, but the writing procedure becomes slower due to large internal resistance
Solution Approach 1:
The patent separates compensation operation and data writing operation into distinct time periods. During compensation period, high potential (Vdata+Vth or Vdd+Vth) is applied to achieve accurate threshold voltage compensation. During subsequent data writing period, the transistor is switched to saturation mode with reduced internal resistance, enabling faster charging. This periodic separation eliminates the time loss caused by high resistance during compensation.
Solution Approach 2:
The patent dynamically changes the operating state of the transistor from diode-connection (during compensation with high potential) to saturation mode (during data writing). This dynamic transition allows the system to achieve compensation accuracy when needed while minimizing charging time during data writing by reducing internal resistance through state change.
Data Source
AI summary
There is provided a pixel circuit, a driving method thereof and a display apparatus. The pixel circuit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistors, a sixth transistor, a seventh transistor, a storage capacitor and a light-emitting element, it can solve the problem that a large difference exists between the data output from the Integrated Circuit and the data actually written to the pixel circuit and avoid the effect that the inconsistency or drift of the threshold voltage (Vth) of the third transistor and the IR drop of the initial voltage (V_initial) have on the current flowing through the light-emitting element.