Pixel Circuitry for Accurate Voltage Storage in Organic EL Displays
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Solution Overview
Problem
Conventional organic EL display devices face challenges in accurately storing signal voltage potential between the gate and source of n-type driving TFTs, leading to variations in capacitor voltage and improper luminescence, which affects image display accuracy.
Innovation Solution
The implementation of a pixel circuitry with a luminescence element, a first capacitor to hold voltage, a driving element connected to the luminescence element, and a second capacitor, along with switching elements and a driving circuit that controls the flow of currents to prevent voltage variations, ensuring accurate potential storage and luminescence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel circuitry with n-type driving TFT is used, then the device can be manufactured with standard processes, but the capacitor voltage varies due to current flow through reference power source lines and signal lines, leading to improper luminescence
Solution Approach 1:
The pixel circuit is divided into multiple independent current paths: a signal line path, a reference power source line path, and a second reference power source line path. By segmenting the current flow paths, the invention prevents current from flowing through the capacitor during the on-state of the third switching element, thereby stabilizing the capacitor voltage and improving luminescence accuracy.
Solution Approach 2:
A fourth switching element is introduced as an intermediary component to control the connection between the second electrode of the capacitor and the second reference power source line. This intermediary switching element ensures that current flows through dedicated reference lines rather than through the signal line or power source lines during normal operation, preventing voltage variations in the capacitor.
2Ease of operation
If current flows through reference power source lines and signal lines during switching, then the switching element can be controlled, but voltage variations occur in the capacitor, affecting image display accuracy
Solution Approach 1:
The invention dynamically controls the state of the fourth switching element based on the operational phase: during the charging phase, the fourth switching element is off to isolate the capacitor from the second reference power source line; during the discharge/holding phase, the fourth switching element is on to maintain the capacitor voltage. This dynamic switching ensures both ease of control and precision in potential storage.
Solution Approach 2:
The capacitor is pre-charged to the signal voltage potential before the third switching element is turned on. This preliminary charging action, performed while the fourth switching element is off, ensures that the capacitor is ready to hold the correct potential without being affected by subsequent current flows through the reference power source lines or signal lines.
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 allows for precise storage of signal voltage potential, enabling highly accurate image display by preventing current flow through reference power source lines and signal lines, thus stabilizing the voltage between the gate and source of the driving TFT.
Implementation Method 1
a first capacitor which holds a voltage
Implementation Method 2
causes the second capacitor to hold a source potential of the driving element
Implementation Method 3
an organic EL element 505 having a cathode connected to a negative power source line
Data Source
AI summary
An image display device includes a driver having a gate connected to a first electrode of a first capacitor and a source connected to an anode of a luminescence element. A second capacitor is connected to a second electrode of the first capacitor. A first switch supplies a reference voltage to the first electrode of the first capacitor. A second switch supplies a signal voltage to the second electrode of the first capacitor. A third switch connects the anode of the luminescence element to the second capacitor. A method of controlling the image display device includes: supplying the signal voltage to the first capacitor by switching ON the first and second switches when the third switch is OFF; switching OFF the first and second switches to turn ON the third switch after the first capacitor holds a capacitor voltage; and causing the second capacitor to hold a source potential of the driver while the third switch is ON.