AMOLED Pixel Driving Circuit Parasitic Capacitance Compensation
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Solution Overview
Problem
The luminance of OLEDs in active matrix displays is affected by parasitic capacitance between the gate and drain of switching TFTs when the scan signal is turned off, leading to inconsistent display quality.
Innovation Solution
An AMOLED pixel driving circuit with a voltage switching module for each row of sub-pixels, which adjusts power supply voltages when switching TFTs are turned on and off, compensating for voltage differences caused by parasitic capacitance to maintain stable current flow through the OLED.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the scan signal is turned off to switch rows in AMOLED display, then row switching is achieved, but parasitic capacitance causes voltage drop and luminance inconsistency
Solution Approach 1:
The patent applies preliminary action by pre-charging the compensation capacitor C10 through the second TFT T20 before turning off the scan signal. This ensures that the gate voltage of T20 is maintained at the correct level even when the parasitic capacitance of T10 causes voltage fluctuations during row switching, thereby preventing luminance inconsistency while achieving fast row switching.
Solution Approach 2:
The patent introduces a compensation capacitor C10 as an intermediary element between the first TFT T10 and the OLED. This capacitor compensates for the voltage fluctuations caused by parasitic capacitance during row switching, acting as a mediator that stabilizes the gate voltage of T20 and ensures consistent luminance across different rows.
2Device complexity
If conventional 2T1C structure is used, then device complexity is reduced, but parasitic capacitance affects display quality
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitance into a beneficial one by using the second TFT T20 in a diode connection mode. The parasitic capacitance that would normally cause voltage drop is instead utilized to maintain the gate voltage of T20 at the correct level during row switching, thereby improving display quality while maintaining the simple 2T1C structure.
Solution Approach 2:
The patent changes the operating parameters of the second TFT T20 by connecting it in diode mode (gate connected to drain). This parameter change allows T20 to function as both a driving transistor and a compensation element, enabling the circuit to compensate for parasitic capacitance effects without adding more transistors or capacitors, thus maintaining low complexity while improving reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures stable current flow and improved display consistency by compensating for voltage changes due to parasitic capacitance, enhancing the overall display quality by maintaining consistent luminance across sub-pixels.
Implementation Method 1
due to the storage function of the capacitor C10, the gate voltage of the second TFT T20 can continue to maintain at the data signal voltage
Implementation Method 2
there is a parasitic capacitance between the gate and the drain of the first TFT T10, and at the instant when the scan signal Gate is changed from a high voltage to a low voltage to turn off the first TFT T10, the drain voltage of the first TFT T10, i.e., the gate voltage of the second TFT T20, will drop due to the existence of parasitic capacitance
Data Source
AI summary
The invention provides an AMOLED pixel driving circuit and method. The AMOLED pixel driving circuit is disposed with a voltage switching module corresponding to each row of sub-pixels, and the voltage switching module is connected to a corresponding row of sub-pixels and scan line corresponding to the row of sub-pixels. The scan signal on the scan line controls the corresponding voltage switching module to provide different power supply voltages to the row of sub-pixels when the switching TFTs in the corresponding row of sub-pixels are turned on and off, thereby compensating for the voltage difference change caused by the parasitic capacitance between the drain and the gate of the switching TFT when the switching TFT changes from on to off, ensuring a stable current flowing through the OLED, and improving the display consistency of the sub-pixels to ensure display quality.