Pixel Circuit Duty Cycle Modulation for Low Gray Levels
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Solution Overview
Problem
Display apparatuses with self-emitting devices face challenges in expressing fine low gray levels due to the number of transistors in pixel circuits, leading to low process efficiency and difficulty in applying existing methods for increasing grayscale resolution.
Innovation Solution
A display apparatus with a pixel circuit configuration that includes node controllers, a driving transistor, and a light emitting device, where the driving transistor is on-duty-driven during one period and off-duty-driven during another, allowing for pulse width modulation to control the light emitting device's emission based on data voltage and gate signals, enhancing grayscale expression by adjusting the on/off timing and duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pixel circuits with multiple transistors are used to increase grayscale resolution, then low grayscale expression is improved, but process efficiency decreases and device complexity increases
Solution Approach 1:
The patent changes the driving parameters by implementing dual-duty-cycle control where the light emitting device operates with different on-duty ratios in different time periods. During the first period, it operates with a first on-duty ratio, and during the second period, it operates with a second on-duty ratio. This parameter change enables fine grayscale control without increasing transistor count, as the grayscale is controlled by temporal duty cycle modulation rather than complex circuit configurations
Solution Approach 2:
The patent applies periodic action by dividing the frame into multiple periods with different duty cycles. The light emitting device is driven periodically with varying on/off patterns - during the first period it emits with a certain duty cycle, and during the second period it emits with a different duty cycle. This periodic modulation enables precise grayscale expression through time-based control rather than requiring additional transistors for voltage level control
2Measurement precision
If more transistors are added to pixel circuits to achieve fine grayscale control, then measurement precision of gray levels is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent replaces the mechanical/circuit-based grayscale control (using multiple transistors and voltage dividers) with a temporal control mechanism. Instead of using additional transistors to create different voltage levels for grayscale, the invention uses time-based duty cycle modulation where the average brightness is controlled by the ratio of on-time to total period. This substitution of spatial control (multiple transistors) with temporal control (duty cycle) simplifies the circuit and improves manufacturability while maintaining precise grayscale resolution
3Device complexity
If conventional driving methods are used with self-emitting devices, then device simplicity is maintained, but low grayscale expression capability is insufficient
Solution Approach 1:
The patent introduces dynamic control by varying the duty cycle of the light emitting device throughout the frame period. Instead of a static on/off control, the driving transistor dynamically adjusts the on-duty ratio in different periods - using a first on-duty ratio during the first period and a second on-duty ratio during the second period. This dynamic temporal modulation enables fine grayscale control while maintaining a simple pixel circuit structure without additional transistors
Data Source
AI summary
A display apparatus includes pixels. Each of the pixels includes a first node controller applying a data voltage to a first node, a second node controller shifting a voltage of a second node from a low level driving voltage to an on pulse voltage, a third node controller applying a reference voltage having an on level to a third node during a first period in one frame and applying the low level driving voltage to the third node during a second period, a driving transistor being on-duty-driven during the first period and off-duty-driven during the second period, and a light emitting device including an anode electrode connected to the second electrode of the driving transistor and a cathode electrode. The light emitting device emits light responsive to a constant current applied from the driving transistor during the first period and does not emit light during the second period.