Diode Current Sensing for Display Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electronic display devices, such as OLED and LED displays, face non-uniformity issues due to process variations, temperature gradients, and aging, leading to visible anomalies and reduced image quality.
Innovation Solution
Implementing a system that uses current sensing across diodes to compensate for operational variations by measuring and adjusting pixel currents to match target values, stored in a lookup table, without user detection, thereby enhancing display panel uniformity and image fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If display compensation is performed using traditional sensing methods, then pixel non-uniformity can be corrected, but the compensation accuracy is insufficient due to inability to directly measure diode current
Solution Approach 1:
The patent introduces an intermediary sensing diode that is electrically coupled to the display diode through a current mirror circuit. This sensing diode acts as a mediator to indirectly measure the current through the display diode by measuring the current through itself, which is a scaled version of the display diode current. The current mirror circuit (using transistors Q1-Q4) serves as the intermediary mechanism that transfers the measurement function from the display diode to the sensing diode, enabling accurate current measurement without directly interfering with the display diode operation.
2Loss of information
If test voltages are applied to determine diode characteristics, then compensation data can be obtained, but visible artifacts may appear during the sensing operation
Solution Approach 1:
The patent applies local quality by using a dedicated sensing diode (D1) that is electrically coupled to but physically separate from the display diode (D2). The sensing operation is localized to the sensing diode, allowing test voltages to be applied to D1 without causing visible artifacts on the display. The sensing diode has the same characteristics as the display diode but serves a different function (measurement vs. display), enabling local measurement operations without affecting the overall display quality.
Solution Approach 2:
The sensing diode serves as an intermediary that allows compensation data to be obtained without directly testing the display diode. By measuring the current-voltage characteristics of the sensing diode (which mirrors the display diode characteristics), the system can acquire the necessary compensation data without applying test voltages to the actual display elements, thus avoiding visible artifacts during sensing operations.
3Measurement precision
If current sensing is implemented across the display diode, then measurement accuracy improves, but the system complexity increases due to additional sensing circuitry
Solution Approach 1:
The sensing diode and its associated circuitry serve multiple functions: (1) it acts as a test object for measuring diode characteristics, (2) it functions as a current sensor through the current mirror relationship, (3) it provides compensation data for both current and voltage compensation operations, and (4) it can be used to characterize temperature and aging effects. This multi-functionality reduces the need for separate dedicated sensing components, thereby limiting the increase in system complexity while achieving accurate current measurement.
Data Source
AI summary
A current-voltage (IV) relationship of a pixel having a diode is initially determined. A first voltage is determined that does not cause the diode to emit light, and a first current across the diode is sensed by applying the first voltage. A predetermined current is determined based on the first voltage and the IV relationship. A ratio is determined based on the first current, a target current, and the predetermined current. A ratio voltage is determined by applying the ratio to a predetermined target voltage. If the first current is less than the predetermined current, then the ratio voltage is applied to supply a target current to the diode. If the first current is greater than the predetermined current, then a second voltage is determined by averaging the first test voltage and the ratio voltage, and the second voltage is applied to supply the target current to the diode.