PWM Pixel Circuit With Constant Current Setting for High-Contrast Displays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing display devices face complexity in controlling light-emitting devices to be in a non-emission state during a constant current setting period, which complicates the circuit configuration and affects image contrast.
Innovation Solution
A display device with a simple circuit configuration that includes a transistor to selectively turn off the light-emitting diode during the constant current setting period, utilizing a minimum number of transistors and capacitors for each pixel circuit, enabling constant current PWM driving and pulse width modulation to control emission states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple resistor is used for current control in OLED display, then the structure is simple, but the current cannot be controlled constantly due to threshold voltage shifts and aging
Solution Approach 1:
The patent implements a feedback mechanism where the drive circuit monitors the actual current through the OLED and adjusts the gate voltage dynamically to compensate for threshold voltage shifts and aging effects, ensuring constant current control despite device degradation over time
Solution Approach 2:
The drive circuit dynamically adjusts operating parameters including gate voltage and reference voltage based on real-time conditions, transitioning from static resistor-based control to dynamic electronic control that adapts to changing device characteristics
2Reliability
If transistor-based current control is used to achieve constant current, then current control stability improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The drive circuit is designed to perform multiple functions including current control, threshold voltage compensation, and aging compensation using a unified circuit architecture that integrates these functions rather than requiring separate dedicated circuits for each function
Solution Approach 2:
The circuit compensates for threshold voltage shifts and aging by dynamically changing operating parameters such as gate voltage and reference voltage levels, allowing the same circuit structure to maintain constant current control despite changing device characteristics
3Reliability
If higher drive voltage is applied to compensate for threshold voltage shifts, then current control stability improves, but power consumption increases
Solution Approach 1:
The feedback mechanism monitors actual OLED current and adjusts gate voltage precisely to maintain constant current operation, preventing excessive voltage application and minimizing power consumption while still compensating for threshold shifts and aging
Solution Approach 2:
The circuit applies only the necessary voltage adjustment needed for compensation rather than using excessive high voltage, achieving sufficient compensation with minimal energy input to avoid unnecessary power consumption
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A display device includes a plurality of pixel circuits each including: a light-emitting element; a pulse width modulation (PWM) controller configured to control whether to supply current to the light-emitting element; and a constant current controller configured to supply the current to the light-emitting element, wherein the constant current controller, the PWM controller, and the light-emitting element are connected in series between a first power line and a second power line to supply the current to the light-emitting element; and a transistor configured to turn off the light-emitting element during a constant current setting period is provided between the first power line and the constant current controller.