Retentive Capacitor Threshold Correction in Active Matrix Displays
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Solution Overview
Problem
Active matrix planar self-emission display apparatuses face challenges due to transistor threshold voltage and mobility variations, as well as organic EL device characteristic fluctuations, which affect light emission luminance and hinder high-definition display capabilities.
Innovation Solution
The display apparatus incorporates a pixel array with a driver that includes a main scanner, power supply scanner, and signal selector, utilizing a retentive capacitor to correct threshold voltage and mobility variations by supplying power supply voltage as switching pulses, reducing the number of components and interconnects, and enabling accurate potential switching between signal and reference potentials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If characteristic fluctuation correcting function is added to each pixel circuit, then light emission luminance uniformity is improved, but pixel circuit structure becomes complex
Solution Approach 1:
The patent combines the characteristic fluctuation correcting function with the existing pixel circuit components. The retentive capacitor is used to store both the signal potential and the threshold voltage correction value, eliminating the need for separate correcting circuits. The sampling transistor serves dual purposes: sampling the signal potential and participating in the threshold voltage correction process through feedback from the retentive capacitor.
Solution Approach 2:
The pixel circuit performs self-correction of threshold voltage variations using its own internal components. The feedback path from the retentive capacitor to the sampling transistor gate creates a self-regulating system that automatically compensates for transistor parameter variations without requiring external correction signals or additional control circuits.
2Reliability
If many components and interconnects are used for correction function, then correction capability is improved, but high-definition display capability is hindered
Solution Approach 1:
The patent merges multiple functions into existing components: the retentive capacitor stores both signal and correction data, the sampling transistor performs both signal sampling and correction participation, and the feedback path uses existing interconnects. This reduces the number of additional components needed while maintaining correction capability.
Solution Approach 2:
Existing pixel circuit components are given multiple functions: the retentive capacitor serves as both signal storage and correction value storage, the sampling transistor serves as both signal sampling and correction feedback, and the feedback path serves as both signal routing and correction signal transmission. This multi-functionality reduces overall circuit complexity.
3Manufacturing precision
If threshold voltage correcting process is repeated multiple times, then correction accuracy is improved, but time consumption increases
Solution Approach 1:
The threshold voltage correcting process is implemented as a periodic feedback mechanism that operates during specific time intervals within each horizontal period. The correction is applied iteratively but efficiently, utilizing the existing scanning and signal supply timing to perform multiple correction cycles without significantly extending the overall display refresh time.
Data Source
AI summary
A scanner repeats a threshold voltage correcting process over a plurality of horizontal periods prior to the sampling of a signal potential to hold a voltage corresponding to the threshold voltage of a driving transistor reliably in a retentive capacitor. Each signal line is associated with a pair of switches, one for supplying the signal potential to the signal line and the other for connecting, to the signal line, a common line for supplying a reference potential. A signal selector turns on and off the switches in each horizontal period in timed relation to a line sequential mode to switch between the signal potential and the reference potential and selectively supply the signal potential and the reference potential to the signal line of each column.