Pixel Circuit Current Compensation for Display Brightness
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Solution Overview
Problem
Conventional light emitting displays cannot emit light with desired brightness due to variations in transistor threshold voltages across pixels, and lack a method to measure and control the current flowing in each pixel accurately.
Innovation Solution
A pixel circuit is designed with a driver that supplies a pixel current corresponding to a data signal, using switching units and capacitors to adjust the current and compensate for transistor threshold voltages, allowing for the generation of a desired pixel current and display of images with desired brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If transistors are provided in each pixel for supplying current corresponding to data signal, then the light emitting device can emit light, but the brightness cannot be controlled accurately due to threshold voltage variations
Solution Approach 1:
The patent implements a feedback mechanism where the actual pixel current is measured and compared with the target current, and the data signal is adjusted based on the comparison result. The data driver measures the pixel current through the data line, compares it with the target current corresponding to the input data signal, and feeds back an adjusted data signal to achieve accurate current control despite transistor threshold voltage variations.
Solution Approach 2:
The patent replaces direct electrical current control through transistor gating with a measurement and feedback-based control system. Instead of relying solely on the transistor's electrical characteristics to control current, the system measures the actual current flow and uses feedback to adjust the control signal, substituting pure electrical control with a measurement-feedback mechanism.
2Ease of manufacture
If transistors with different threshold voltages are used in pixels, then manufacturing is simplified, but the pixel current varies and image brightness becomes inconsistent
Solution Approach 1:
The feedback mechanism measures the actual pixel current for each pixel and compares it with the target current. Based on the comparison, the data driver adjusts the data signal to compensate for threshold voltage variations, ensuring that pixels with different transistor characteristics still produce consistent brightness levels.
Solution Approach 2:
The patent changes the data signal parameter dynamically based on feedback from current measurement. Instead of using a fixed data signal, the system adjusts the voltage or current level of the data signal according to the measured pixel current, thereby compensating for manufacturing variations in transistor threshold voltages.
3Adaptability or versatility
If switching units are added to control current flow, then current adjustment capability is improved, but circuit complexity increases
Solution Approach 1:
The data line serves multiple functions: it supplies data signals to pixels during normal operation and also serves as a measurement path for pixel current. The switching units are integrated into the existing pixel structure and serve both as current control elements and as part of the measurement circuitry, reducing the need for separate dedicated components.
Solution Approach 2:
The pixel circuit itself provides the measurement capability by utilizing its own current path. The current that flows through the pixel for display purposes is the same current that is measured for feedback, eliminating the need for separate measurement circuits and reducing overall system complexity.
4Manufacturing precision
If current measurement and control is implemented for each pixel, then image quality is improved, but the device complexity and power consumption increase
Solution Approach 1:
The data driver performs multiple functions: it generates data signals, measures pixel currents through the data lines, compares measured currents with target currents, and outputs adjusted data signals. By integrating these functions into a single driver circuit rather than having separate circuits for each function, the overall device complexity is managed while achieving precise current control.
Solution Approach 2:
The patent merges the data signal supply function and the current measurement function into a single integrated system. The data line serves dual purposes as both a signal carrier and a measurement path, and the data driver integrates signal generation, measurement, comparison, and adjustment functions, reducing the number of separate components needed.
Data Source
AI summary
Circuits for a pixel in a light emitting display capable of displaying an image with desired brightness are described. The pixel circuit includes a driver to supply a pixel current to the light emitting device corresponding to a data signal supplied from a data line, a first switching unit coupled between the driver and the data line, and a second switching unit coupled between the data line and a common node formed between the driver and the light emitting device. The driver, in turn, includes a first transistor to generate the pixel current to be supplied from a first power line to the light emitting device, a first capacitor coupled between the first transistor and the first switching unit to be charged with a voltage corresponding to the threshold voltage of the first transistor, and a second capacitor to be charged with a voltage corresponding to the data signal.