Display Module PWM Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Existing display modules using inorganic light emitting elements face challenges in achieving low power consumption and maintaining color reproducibility due to variations in threshold voltage of driving transistors and changes in wavelength with driving current amplitude.
Innovation Solution
A display module with a pixel circuit comprising a constant current generator and a PWM circuit, where the PWM circuit includes a depletion mode driving transistor with a threshold voltage compensation mechanism, allowing for stable and efficient driving of inorganic light emitting elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If active matrix driving is used to reduce power consumption, then power efficiency is improved, but threshold voltage variation of driving transistors causes deterioration of display uniformity
Solution Approach 1:
The patent applies preliminary action by measuring and storing the threshold voltage of each driving transistor before normal display operation. The pixel circuit performs threshold voltage compensation in advance during an initialization phase, ensuring that subsequent display operations maintain uniformity despite transistor parameter variations. This pre-measurement and pre-compensation approach resolves the contradiction by preparing the system beforehand to counteract the worsening effect.
2Illumination intensity
If pulse amplitude modulation is used to control subpixel gradation, then brightness control is achieved, but wavelength changes with current amplitude causing color reproducibility deterioration
Solution Approach 1:
The patent employs periodic action by using pulse width modulation instead of amplitude modulation. The constant current source maintains a fixed amplitude, and gradation is achieved by varying the pulse width (duration) periodically. This periodic control method ensures that the current amplitude remains constant, preventing wavelength shifts, while still achieving brightness control through temporal integration of light perception. This resolves the contradiction by decoupling brightness control from amplitude variation.
3Area of stationary object
If inorganic light emitting elements are used in large-sized display panels, then display area is increased, but threshold voltage variations across the panel cause color inconsistency
Solution Approach 1:
The patent applies segmentation by dividing the large display panel into multiple independent pixel circuits, each with its own threshold voltage measurement and compensation mechanism. Instead of treating the entire panel as a single system, each pixel or subpixel circuit independently measures its driving transistor's threshold voltage and applies compensation. This segmented approach ensures that local variations in threshold voltage across the large panel area do not compromise overall color consistency.
Data Source
AI summary
A display module may include a plurality of pixels, wherein each of the plurality of pixels includes a plurality of subpixels of different colors that are disposed in a matrix form. Each of the plurality of subpixels includes an inorganic light emitting element, a constant current generator which provides a constant current to the inorganic light emitting element, and a pulse width modulation (PWM) circuit which includes a first depletion mode driving transistor, and controls a time during which the constant current flows through the inorganic light emitting element based on a PWM data voltage applied to a gate terminal of the first depletion mode driving transistor and a threshold voltage of the first depletion mode driving transistor.