Display Pixel Circuit Using Ramp Voltage Comparator for Color Shift Prevention
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Solution Overview
Problem
Display devices using micro light emitting diodes (μLEDs) or organic light emitting diodes (OLEDs) face image distortion due to color shift phenomena caused by varying driving currents, which affect gray level representation and image quality.
Innovation Solution
A display device with a pixel structure that includes a light emitting element, an initialization circuit, a data writing circuit, a ramp generating circuit, a comparator, and a driving circuit, where a constant current is provided to the light emitting element, and a ramp voltage is generated to determine the emission time based on the data voltage level, preventing color shift and image distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the light emitting element is driven in the PAM method by adjusting the amount of driving current, then the gray level can be represented, but a color shift phenomenon occurs and the image is distorted
Solution Approach 1:
The patent changes the control parameter from driving current amplitude (PAM) to driving current pulse width (PWM). By maintaining a constant current amplitude and varying only the pulse duration, the invention eliminates color shift while preserving gray level representation capability. The comparator generates a ramp voltage that decreases over time, and the emission time is determined by when this ramp voltage intersects with the data voltage, effectively converting amplitude modulation to pulse width modulation.
2Manufacturing precision
If a constant current is provided to the light emitting element, then color shift is prevented, but additional circuits are required to control emission time
Solution Approach 1:
The patent segments the pixel circuit into distinct functional modules: an initialization circuit to set initial voltages, a ramp generating circuit to create the time-varying ramp voltage, a data writing circuit to store the data voltage, and a comparator to determine emission timing. This segmentation allows each module to perform its specific function efficiently, managing the increased circuit complexity through functional decomposition.
Solution Approach 2:
The initialization circuit performs preliminary action by pre-charging the ramp capacitor to a first initialization voltage and setting the data node to a second initialization voltage before the emission phase. This preliminary voltage setup ensures that the ramp voltage starts from a known state and the comparator can accurately determine emission time based on the intersection with the data voltage, eliminating the need for complex reset circuits.
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
The solution prevents color shift and image distortion by maintaining a constant current to the light emitting element and using a ramp voltage to accurately control emission time, thereby enhancing image quality.
Implementation Method 1
A display device may display an image by driving a light emitting element, such as a micro light emitting diode (μLED) or an organic light emitting diode (OLED)
Implementation Method 2
a ramp capacitor connected to the first node, and configured to generate the ramp voltage based on the ramp current
Data Source
AI summary
A display device includes a plurality of pixels, where each of the plurality of pixels includes a light emitting element, an initialization circuit configured to provide a first initialization voltage to a first node, a data writing circuit configured to provide a data voltage to a second node, a ramp generating circuit configured to provide a ramp voltage to the first node in response to an enable signal, a comparator configured to generate an emission signal by comparing the ramp voltage at the first node and the data voltage at the second node, and a driving circuit configured to provide a constant current to the light emitting element in response to the emission signal.