Display Device Driving Circuit PWM Mode Color Shift Reduction
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Solution Overview
Problem
Light-emitting components in display devices experience significant color shift when driven by small currents, leading to poor picture quality, especially at lower gray levels.
Innovation Solution
The display device employs a driving circuit that switches between current mode and pulse width modulation (PWM) mode based on gray levels, using pulse controllable periods and hold periods to maintain stable driving current and reduce color shift, allowing for more efficient light emission and extended PWM periods to support additional gray levels without increasing the frame period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the light emitting component is driven by a small current to achieve lower brightness, then the brightness is reduced, but the color shift becomes significant resulting in poor picture quality
Solution Approach 1:
The patent applies pulse width modulation (PWM) to drive the light emitting component with periodic pulses instead of continuous small current. By controlling the duty cycle of these periodic pulses, the patent achieves lower average brightness while maintaining the light emitting component at a higher, more stable current level during active periods, thereby reducing color shift and improving picture quality
Solution Approach 2:
The patent dynamically switches between different driving modes (current mode and PWM mode) based on the desired gray level. For lower gray levels where color shift is problematic, PWM mode is used to maintain current stability; for higher gray levels, current mode provides sufficient brightness. This dynamic adaptation resolves the contradiction by selecting the appropriate driving strategy for each brightness level
2Adaptability or versatility
If the PWM period is extended to support additional gray levels, then the range of gray levels increases, but the frame period may be exceeded
Solution Approach 1:
The patent segments the PWM period into multiple sub-periods, each responsible for controlling a specific range of gray levels. This segmentation allows the system to manage the extended PWM period in manageable chunks, enabling support for additional gray levels while carefully controlling the total time consumption to fit within the frame period constraint
Solution Approach 2:
The patent introduces a temporal dimension by organizing gray level control across multiple sub-periods within the PWM period. Instead of treating gray level control as a single-dimensional parameter, the patent distributes control across time sub-segments, enabling extended gray level range without proportionally increasing the overall frame period
3Illumination intensity
If the light emitting component is driven by a large current to achieve higher brightness, then the brightness is improved, but the color shift also increases resulting in poor picture quality
Solution Approach 1:
The patent uses PWM to convert continuous large current driving into periodic pulsing. By controlling the duty cycle, the patent achieves the desired average brightness while the light emitting component experiences brief periods of high current followed by off periods. This periodic operation prevents the continuous color shift issues associated with sustained large current while maintaining brightness
Data Source
AI summary
A display device includes a pixel. The pixel includes a light emitting unit and a driving circuit for driving the light emitting unit. When the light emitting unit is driven in a pulse width modulation (PWM) mode with a PWM period, the PWM period includes a plurality of pulse controllable periods.