AMOLED Pixel Circuit Parameter Extraction Using Charge-Pump Amplifier
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Solution Overview
Problem
Active matrix organic light emitting device (AMOLED) displays face challenges in extracting parameters like threshold voltage and mobility of drive transistors and OLEDs due to aging, which affects image quality, and this requires additional components in the driver circuit, reducing pixel aperture.
Innovation Solution
The method involves reading circuit parameters by turning off the drive device, supplying a predetermined voltage to the light emitting device, and measuring the voltage while it's off, using a charge-pump amplifier to isolate and integrate currents, allowing for the extraction of threshold voltage and mobility with minimal components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional components are added to the driver circuit to extract threshold voltage and mobility parameters, then parameter extraction capability is improved, but pixel aperture area is reduced
Solution Approach 1:
The drive transistor serves multiple functions: it acts as both the pixel drive transistor for controlling OLED current and as a measurement transistor for extracting threshold voltage and mobility parameters. By programming the gate with specific voltages, the same transistor is used for both display operation and parameter extraction, eliminating the need for separate measurement components.
Solution Approach 2:
The pixel circuit uses its own drive transistor and existing capacitors to perform self-diagnosis and parameter extraction. The circuit measures its own threshold voltage and mobility characteristics without requiring external measurement equipment or additional on-pixel components, thereby maintaining maximum pixel aperture.
2Reliability
If threshold voltage and mobility parameters are extracted to compensate for aging effects, then image quality is improved, but device complexity increases
Solution Approach 1:
The system performs parameter extraction and compensation in advance by measuring threshold voltage and mobility characteristics during manufacturing or initialization. These extracted parameters are stored and used to pre-program compensation values that maintain image quality throughout the display's operational life, preventing aging effects rather than correcting them in real-time.
Solution Approach 2:
The system extracts threshold voltage and mobility parameters from the drive transistor characteristics and uses this feedback information to adjust programming voltages. This closed-loop approach compensates for aging effects and process variations, maintaining consistent image quality without requiring complex real-time control circuits.
3Measurement precision
If the drive device is turned off to measure voltage for parameter extraction, then measurement accuracy is improved, but power consumption increases
Solution Approach 1:
Parameter extraction measurements are performed periodically during manufacturing or initialization phases rather than continuously during display operation. The drive transistor is turned off only during these brief measurement intervals to capture accurate threshold voltage and mobility data, then returns to normal low-power operation, minimizing overall power consumption while maintaining measurement accuracy.
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
This approach enables efficient extraction of parameters with fewer components, maintaining image quality and maximizing pixel aperture by compensating for aging effects in AMOLED displays.
Implementation Method 1
coupling the pixel circuit to a charge-pump amplifier, isolating the charge-pump amplifier from the pixel circuit to provide a voltage output either proportional to the charge level or integrating the current from the pixel circuit
Data Source
AI summary
A system reads a desired circuit parameter from a pixel circuit that includes a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal. One embodiment of the extraction system turns off the drive device and supplies a predetermined voltage from an external source to the light emitting device, discharges the light emitting device until the light emitting device turns off, and then reads the voltage on the light emitting device while that device is turned off. The voltages on the light emitting devices in a plurality of pixel circuits may be read via the same external line, at different times.