Display Pixel Drive Circuits for Transistor Variation Compensation
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Solution Overview
Problem
Displays with varying drive transistor characteristics due to fabrication nonuniformities or aging lead to image degradation if uncompensated.
Innovation Solution
A pixel drive and sense circuit with compensation coefficients adjusts gate-source voltage to counteract transistor mobility and threshold voltage variations, using a 4T1C drive circuit with a drive amplifier and sensing circuit to iteratively refine coefficients for precise current control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If drive transistor characteristics are not compensated, then device complexity is reduced, but image quality degrades due to pixel nonuniformities
Solution Approach 1:
The drive transistor itself is used to generate the compensation coefficient by sensing its own current characteristics. The transistor's current flow through the sensing circuit during the sensing phase directly provides the information needed for compensation, eliminating the need for external characterization circuits and achieving self-compensation.
Solution Approach 2:
The sensing circuit and drive circuit are merged into a single integrated structure where the same transistors and capacitors serve dual purposes. The drive transistor acts as both the current source and the sensing element, while capacitors serve as both storage elements and sensing nodes, reducing overall circuit complexity.
2Manufacturing precision
If compensation coefficients are stored in non-volatile memory per pixel, then manufacturing precision is improved, but device complexity and memory requirements increase
Solution Approach 1:
A single non-volatile memory structure serves multiple pixels by time-multiplexed operation. The memory is sequentially programmed and read for different pixels during different time phases, allowing one memory unit to compensate for multiple pixels without requiring dedicated memory per pixel.
Solution Approach 2:
Compensation coefficients are pre-calculated and stored in non-volatile memory during a characterization phase before normal display operation. This preliminary programming allows the display to operate with simplified real-time control, as the complex coefficient calculation is performed in advance.
3Measurement precision
If sensing phase duration is increased, then measurement precision of current characteristics is improved, but productivity decreases due to longer pixel drive cycle
Solution Approach 1:
The sensing operation is performed periodically at specific phases within the pixel drive cycle rather than continuously. By scheduling sensing during dedicated time windows and using time-multiplexed operation across pixel rows or columns, the system achieves accurate measurements without preventing normal display operation.
Solution Approach 2:
The display continues to refresh and update during the sensing phase by using different pixel rows or columns for sensing versus display at different times. This time-multiplexed approach ensures that useful display action continues without interruption while still allowing periodic sensing operations.
Data Source
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AI summary
A system and method for estimating and using pixel compensation coefficients is provided. In some embodiments, the method includes, during a first time interval: comparing a first pixel current for a pixel of the display with a first reference current, to obtain a first pixel current error signal, the first pixel current error signal being the sign of a difference between the first pixel current and the first reference current; and updating one or more compensation coefficients for the pixel, based on the first pixel current error signal.