Display Pixel Circuit Current Path for Contrast
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Solution Overview
Problem
Conventional display devices with organic EL elements experience reduced contrast due to light emission during non-light emission periods, caused by the anode potential exceeding the threshold voltage, leading to constant luminance regardless of signal gradation.
Innovation Solution
A display device with a pixel circuit comprising a P channel type driving transistor, a sampling transistor, a light emission control transistor, a holding capacitor, and an auxiliary capacitor, where a current path directs the driving transistor's current into a predetermined node during non-light emission periods, preventing light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a P channel type transistor is used as a driving transistor for driving the light emitting unit, then the pixel circuit can be configured with a sampling transistor, a light emission control transistor, a holding capacitor, and an auxiliary capacitor, but the anode potential of the light emitting unit exceeds the threshold voltage during non-light emission periods, causing the light emitting unit to emit light at constant luminance regardless of signal gradation, resulting in reduced display contrast
Solution Approach 1:
The pixel circuit is divided into distinct functional components: a driving transistor for current control, a sampling transistor for signal input, a light emission control transistor for timing control, and capacitors for voltage holding. This segmentation allows independent optimization of each component's function to achieve both ease of operation and high contrast by preventing unwanted light emission during non-emission periods
Solution Approach 2:
The light emission control transistor acts as an intermediary between the driving transistor and the light emitting unit. It controls the timing of current flow to the light emitting unit, ensuring that current is only supplied during intended light emission periods and preventing anode potential from exceeding the threshold voltage during non-emission periods, thereby maintaining display contrast
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 configuration ensures the light emitting unit remains in a non-light emission state, enhancing the display panel's contrast by preventing unnecessary light emission during non-emission periods.
Implementation Method 1
an organic EL element is known that utilizes a phenomenon that an organic thin film emits light by using electro luminescence (EL) of an organic material when an electric field is applied thereto
Data Source
AI summary
Provided is a display device in which a pixel circuit is arranged, the pixel circuit including a P channel type driving transistor that drives a light emitting unit, a sampling transistor that samples a signal voltage, a light emission control transistor that controls light emission/non-light emission of the light emitting unit, a holding capacitor that is connected between a gate electrode and a source electrode of the driving transistor, and holds the signal voltage written by the sampling by the sampling transistor, and an auxiliary capacitor that is connected between the source electrode of the driving transistor and a node having fixed potential, the display device including: a current path that flows a current flowing in the driving transistor in a non-light emission period of the light emitting unit into a predetermined node.