Pixel Circuit Switching to Block Voltage Ripple Crosstalk
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Solution Overview
Problem
In organic light emitting display devices, fluctuations in gate-source voltage due to parasitic capacitance and low potential voltage ripples cause image quality deterioration, including horizontal crosstalk and luminance changes, which affect the display's contrast and color reproducibility.
Innovation Solution
A pixel circuit design that includes two switch elements between the driving element and the light emitting element, with one switch element connected to the anode electrode turned off during sensing to block ripple influence, and a compensation step with a reference voltage applied to the source node of the driving element to alleviate hysteresis and luminance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common low potential voltage source is used for multiple pixels, then device complexity is reduced, but image quality deteriorates due to voltage ripples causing horizontal crosstalk
Solution Approach 1:
The common low potential voltage source is segmented into pixel-specific paths by introducing first and second switch elements in each pixel circuit. These switch elements isolate individual pixels from voltage ripples on the shared power line, allowing the common voltage source to maintain low complexity while preventing horizontal crosstalk and image quality deterioration.
2Ease of operation
If the switch element connected to anode electrode is kept on during sensing, then circuit operation is simplified, but ripple influence propagates causing horizontal crosstalk
Solution Approach 1:
The switch elements are dynamically controlled with different timing for sensing and light emission operations. During sensing, the first switch element is turned off to block ripple propagation, while during light emission it is turned on to enable normal circuit operation. This dynamic switching resolves the contradiction between operational simplicity and preventing harmful ripple effects.
3Speed
If gate-source voltage is allowed to fluctuate with OLED influence, then device response is fast, but luminance stability deteriorates causing image quality issues
Solution Approach 1:
A compensation step is introduced before the light emission step to pre-adjust the gate-source voltage of the driving element. This preliminary compensation accounts for expected voltage drops and OLED influences, ensuring that the actual luminance output remains stable while maintaining fast response characteristics during the light emission phase.
Data Source
AI summary
A pixel circuit and a display device including the pixel circuit are discussed. The pixel circuit can include a driving element including a first electrode connected to a first node to which a pixel driving voltage is applied, a gate electrode connected to a second node, and a second electrode connected to a third node; a first switch element including a first electrode connected to the third node, a gate electrode to which a first light emission control pulse is applied, and a second electrode connected to a fourth node; a second switch element including a first electrode connected to the third node, a gate electrode to which a second light emission control pulse is applied, and a second electrode connected to a fifth node; and a light emitting device including an anode connected to the fifth node, and a cathode electrode to which a low potential power voltage is applied.