Pixel Circuit Voltage Fluctuation Compensation in SSD Displays
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Solution Overview
Problem
Active-matrix organic EL display devices employing the SSD scheme face a 'field through phenomenon' where the voltage held in data lines fluctuates due to parasitic capacitance, leading to inadequate image display and increased power consumption when trying to compensate for these fluctuations.
Innovation Solution
The display device incorporates a pixel circuit with a voltage holding capacity, an input transistor, a drive transistor, a monitor control transistor, and a voltage fluctuation compensation transistor, along with corresponding drive circuits, to measure and compensate for voltage fluctuations in data lines, using a voltage fluctuation compensation line to cancel out changes in data line voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the SSD scheme is employed to drive more data lines, then the display device can achieve higher definition and larger size, but voltage fluctuations occur in data lines due to parasitic capacitance
Solution Approach 1:
A compensation capacitor is introduced as an intermediary element connected in parallel with the parasitic capacitance of the data line. This capacitor serves as a mediator to store and release charge, compensating for the voltage fluctuations caused by the parasitic capacitance during SSD operation.
Solution Approach 2:
The invention changes the electrical parameters of the data line by adding a compensation capacitor, which modifies the capacitance value to counterbalance the parasitic capacitance effect. This parameter change enables the data line to maintain stable voltage during the SSD driving scheme.
2Stability of the object's composition
If pre-correction of analog data signals is applied to compensate for voltage fluctuations, then voltage stability improves, but power consumption increases
Solution Approach 1:
The compensation capacitor provides self-service by automatically compensating for voltage fluctuations through its inherent charge storage and release characteristics. The circuit utilizes the natural electrical properties of the capacitor to counteract parasitic capacitance effects without requiring external correction signals or additional power consumption.
Solution Approach 2:
The invention converts the harmful effect of parasitic capacitance into a beneficial phenomenon by using the same capacitance principle to create a compensation capacitor. The parasitic capacitance, which causes voltage fluctuations, is counteracted by an equal and opposite capacitance effect from the compensation capacitor, turning the harmful electrical property into a useful compensating mechanism.
3Measurement precision
If more transistors are added to measure drive current, then measurement precision improves, but device complexity increases
Solution Approach 1:
The monitor transistor is designed with multi-functionality, serving both as a switching element for the drive current path and as a measurement instrument. By configuring the transistor and compensation capacitor to work together, the circuit achieves drive current measurement without requiring separate dedicated measurement transistors, thus reducing overall device complexity.
Solution Approach 2:
The invention implements feedback by using the compensation capacitor to sense voltage changes caused by drive current variations and automatically adjusting the charge storage to maintain stable voltage. This feedback mechanism enables accurate drive current measurement through the existing transistor structure without adding complexity.
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 effectively suppresses voltage fluctuations in data lines, reducing the need for pre-correction of analog data signals and minimizing power consumption, while accurately measuring drive currents and preventing leakage currents in unmeasured pixel circuits.
Implementation Method 1
a voltage fluctuation compensation capacity formed between the first conduction terminal in the voltage fluctuation compensation transistor and the control terminal in the voltage fluctuation compensation transistor
Data Source
AI summary
The purpose of the present invention is to suppress the fluctuation of a data line voltage that occurs when an analog voltage signal is sampled and held in a data line in a display device provided with a current-driven display element. Transistors (SWr, SWG, SWb) of each demultiplexer (252) are successively switched on, for each predetermined period, in a selection period of a write control line (SW_LR(i)). In a period when the transistor (SWr) is switched on, an analog video signal (Dj) from a data voltage output unit circuit (211d) is applied to a data line (SLrj) and a pixel circuit (50r). When the transistor SWr is then switched off, the voltage held by the data line (SLrj) decreases below the voltage of the analog video signal (Dj) due to a parasitic capacitance (Cssdr). However, the voltage of a voltage fluctuation compensation line (G3_Cnt (i)) changes from a low level to a high level within the selection period. This causes the voltage of the data line (SLrj) to rise via a capacitor (Ccnt), and the decrease in voltage to be compensated for.