Display Pixel Circuit Using Reference Voltage for Threshold Compensation
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Solution Overview
Problem
Display devices, such as OLEDs, suffer from luminance non-uniformity due to varying threshold voltages of driving transistors, which is not adequately addressed by existing compensation methods requiring initialization signals.
Innovation Solution
A pixel design that utilizes a capacitor and transistors to perform threshold voltage compensation without an initialization signal, using reference and data voltages to control the fourth transistor's state, reducing the need for additional signal lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an initialization signal is used to initialize the gate node before applying data voltage, then the gate node can be properly initialized to an initialization voltage lower than the data voltage, but the number of signal lines increases and the device complexity increases
Solution Approach 1:
The patent extracts and eliminates the initialization signal from the system by redesigning the transistor configuration. The fourth transistor's gate is connected to the second node instead of receiving a separate initialization signal, allowing the initialization function to be achieved through the interaction of existing signals (reference voltage and data voltage) with the transistor network, thereby removing the need for an additional signal line.
Solution Approach 2:
The second node serves multiple functions: it receives the reference voltage during the initialization period, transfers the data voltage during the data writing period, and controls the fourth transistor's state based on the voltage level. This multi-functionality eliminates the need for dedicated initialization signal lines while maintaining the initialization capability.
2Reliability
If a diode-connected driving transistor is used to transfer data voltage to the gate node, then threshold voltage compensation is achieved, but the gate node must be initialized to a voltage lower than the data voltage, requiring an additional initialization signal
Solution Approach 1:
The patent applies preliminary action by establishing the voltage relationship between the second node and first node through the fourth transistor before data voltage is applied. During the initialization period, the reference voltage is transferred to the second node, which then controls the fourth transistor to transfer initialization voltage to the gate node, preparing the system in advance for data voltage application without requiring a separate initialization signal.
Solution Approach 2:
The fourth transistor acts as an intermediary between the second node (receiving reference/data voltage) and the first node (gate node). It mediates the voltage transfer by being controlled by the voltage level at the second node, automatically enabling initialization voltage transfer when reference voltage is applied and disabling it when data voltage is applied, thus eliminating the need for external initialization signal control.
Data Source
AI summary
A pixel includes a capacitor connected between a first power supply voltage line and a first node, a first transistor including a gate connected to the first node, a first terminal connected to a second node, and a second terminal connected to a third node, a second transistor including a gate receiving a scan signal, a first terminal connected to a data line, and a second terminal connected to the second node, a third transistor including a gate receiving the scan signal, a first terminal connected to the third node, and a second terminal connected to the first node, a fourth transistor including a gate connected to the second node, a first terminal connected to an initialization voltage line, and a second terminal connected to the first node, and a light emitting element connected to the third node and a second power supply voltage line.