Pixel Circuit Brightness Uniformity via Low-Current Charging
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Solution Overview
Problem
Trace impedance in display panels leads to varying voltage attenuations, affecting brightness uniformity in self-luminous display panels, as the current flowing through transistors controlling luminous current is impacted by different voltage drops at different locations.
Innovation Solution
A pixel circuit design that includes a light-emitting device, multiple transistors, and capacitors, where a low-current charging reference voltage is used to write data voltage into capacitors, reducing the influence of trace impedance and enhancing brightness uniformity by minimizing voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel circuit is used with standard current values for charging, then the circuit operation is simple, but the trace impedance causes varying voltage attenuations that affect brightness uniformity
Solution Approach 1:
The patent applies parameter changes by using different current values for charging versus discharging the capacitor. Specifically, a first current value is used during the charging phase and a second current value is used during the discharging phase, where these current values are different. This parameter differentiation compensates for trace impedance effects and improves brightness uniformity across the display panel.
2Manufacturing precision
If the transistor controlling luminous current is operated in saturation region, then the impact of trace impedance is reduced, but different voltage drops at different locations still affect brightness uniformity
Solution Approach 1:
The patent uses different current values for charging and discharging operations to compensate for location-dependent voltage drops. By adjusting the charging current (first current value) differently from the discharging current (second current value), the circuit compensates for trace impedance effects that vary by location, thereby improving brightness uniformity while maintaining voltage stability.
3Speed
If high current is used for charging the capacitor, then the charging speed is fast, but the voltage drop due to trace impedance increases affecting brightness uniformity
Solution Approach 1:
The patent optimizes charging speed while maintaining brightness uniformity by using a first current value for charging that is differentiated from the second current value used for discharging. This parameter differentiation allows the charging current to be optimized for speed while compensating for trace impedance effects, ensuring both fast charging and uniform brightness.
Data Source
AI summary
A pixel circuit includes a light-emitting device, a first transistor, a second transistor, a first capacitor, a third transistor, a fourth transistor, and a fifth transistor. The first transistor and the fourth transistor are controlled by a light-emitting signal. The third transistor and the fifth transistor are controlled by a scan signal. The light-emitting device, the first transistor, the second transistor, the fourth transistor, and the fifth transistor are serially connected between a system high voltage and a system low voltage. The third transistor is coupled between a data signal and a control terminal of the first transistor. The first capacitor is coupled between a control terminal and a downstream terminal of the second transistor. The fifth transistor is coupled between the downstream terminal of the second transistor and a charging reference voltage. A current of the charging reference voltage is less than a current of the system low voltage.