Organic EL Display Drive Circuit with Measurement Element
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Solution Overview
Problem
Active matrix organic EL displays face issues with uneven luminance, burn-in due to non-uniform characteristics of low-temperature polysilicon TFTs, and temperature-induced current changes affecting white balance in full-color displays.
Innovation Solution
Incorporating a self-emissive element for measurement purposes, a drive voltage supply circuit, and a drive state detection circuit to monitor and correct the drive state of organic EL elements, allowing for digital drive and pulsed voltage control, and using a correction circuit to adjust voltage and power supply to maintain appropriate white balance and luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If low-temperature polysilicon TFT is used as drive element, then high mobility and fast response are achieved, but uneven luminance occurs due to non-uniform characteristics in saturated region
Solution Approach 1:
The patent transitions from static voltage drive to dynamic pulsed voltage drive, where the drive voltage is applied in controlled pulses rather than continuously. This dynamic approach allows precise control of current flow through the organic EL elements, compensating for TFT characteristic variations and achieving uniform luminance while maintaining fast response.
Solution Approach 2:
The patent changes the drive voltage parameter from constant to time-varying pulsed signals. By controlling the pulse width, amplitude, and timing, the system can precisely regulate the current through each pixel, compensating for manufacturing variations in TFT characteristics and achieving uniform display across the panel.
2Manufacturing precision
If digital drive is used to improve uniformity, then luminance uniformity is improved, but burn-in appears due to degradation of organic EL elements
Solution Approach 1:
The patent employs periodic pulsed driving instead of continuous or simple digital on/off driving. The organic EL elements are driven with periodic pulses that include appropriate duty cycles and timing, allowing the elements to rest between activations. This periodic action reduces cumulative degradation and prevents burn-in while maintaining uniform luminance through precise pulse control.
Solution Approach 2:
The patent maintains continuous monitoring and adjustment of drive parameters through the measurement element and control circuitry. By continuously adapting the pulse characteristics based on detected luminance levels and element state, the system ensures optimal driving conditions that prevent degradation while maintaining uniform display quality throughout the element's operational life.
3Adaptability or versatility
If full-color display is implemented, then color information is provided, but white balance becomes off-balance due to temperature-induced current changes
Solution Approach 1:
The patent incorporates a measurement element that continuously monitors the drive state and luminance output of the organic EL elements. This feedback information is fed back to the control circuit, which adjusts the pulse drive parameters for each color sub-pixel (R, G, B) to compensate for temperature-induced current variations. This closed-loop feedback system maintains accurate white balance across varying temperatures while preserving full-color display capability.
Solution Approach 2:
The patent segments the drive control into separate channels for each color (R, G, B) and implements independent pulse width and amplitude control for each. The measurement element is also segmented to measure each color channel separately. This segmentation allows precise independent adjustment of each color's drive parameters to compensate for differential temperature effects, maintaining white balance while enabling full-color display.
4Measurement precision
If self-emissive element for measurement is added, then drive state detection is enabled, but device complexity increases
Solution Approach 1:
The patent designs the measurement element to serve multiple functions: it acts as a reference for luminance measurement, a test element for detecting drive state variations, and a calibration standard for white balance adjustment. The same measurement circuitry is used across different operating conditions and temperatures. This multi-functionality reduces the need for separate dedicated components for each measurement task, thereby limiting the increase in device complexity while achieving precise drive state detection.
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 effectively maintains uniform luminance, prevents burn-in, and adjusts for temperature-induced current changes, ensuring consistent white balance and extended display lifespan by dynamically controlling the drive current and voltage.
Implementation Method 1
self-emissive elements that emit light in accordance with a drive current
Data Source
AI summary
A display device in which measurement emissive elements that emit light in accordance with a drive current are arranged in a matrix within a display region, the display device includes a measurement emissive element which is formed in a position different from the display region and formed by the same process as the organic EL elements formed in the display region; drive voltage supply circuit for supplying drive voltage to the measurement emissive element; and drive state detection circuit for detecting the drive state of the measurement emissive element in the case where the drive voltage is supplied by the drive voltage supply circuit.