OLED Threshold Voltage Sensing Circuit with Charge-Share Compensation
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Solution Overview
Problem
Organic light emitting diode (OLED) display devices face challenges in maintaining constant brightness due to changes in threshold voltage over time, which existing technologies fail to address effectively, leading to reliability and sensitivity issues in sensing these voltages.
Innovation Solution
A circuit is designed to sense threshold voltages of OLEDs, incorporating a sample and hold unit with capacitors and switching units to reduce parasitic capacitor offsets, and an amplifier to amplify signals, along with an analog-to-digital converter and memory to store digital signals, ensuring consistent brightness by compensating for threshold voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional sample and hold circuit is used to sense threshold voltage, then the circuit structure is simple, but parasitic capacitor offsets reduce sensing reliability and sensitivity
Solution Approach 1:
The sample and hold circuit is divided into multiple stages: a first sample and hold unit for initial voltage sampling, a second sample and hold unit for offset compensation, and a third sample and hold unit for final signal holding. Each stage performs a specific function to progressively improve sensing reliability while managing circuit complexity through functional segmentation.
Solution Approach 2:
Dummy capacitors are introduced as intermediary elements to compensate for parasitic capacitor offsets. These dummy capacitors are strategically placed to mirror the parasitic effects, allowing the circuit to measure and subtract offset voltages, thereby improving sensing reliability without fundamentally changing the core sample and hold mechanism.
2Illumination intensity
If threshold voltage changes are not compensated, then the device structure remains simple, but OLED brightness varies over time
Solution Approach 1:
The circuit implements feedback by continuously sensing the threshold voltage of the OLED, comparing it against reference values, and adjusting the drive signal accordingly. The sample and hold units capture voltage states at different times, and the differences are used to compensate for threshold shifts, ensuring stable OLED brightness despite aging effects.
Solution Approach 2:
The first sample and hold unit performs preliminary voltage sampling before the OLED is fully driven, capturing the threshold voltage in advance. This preliminary measurement allows the compensation circuit to prepare correction values before actual display operation, improving brightness stability proactively rather than reactively.
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 improves the reliability and sensitivity of threshold voltage sensing, allowing OLEDs to maintain constant brightness despite changes in threshold voltage, thereby enhancing the performance and longevity of OLED display devices.
Implementation Method 1
a first capacitor configured to sample the threshold voltage of the OLED
Implementation Method 2
a second capacitor configured to charge-share a voltage on or from the first capacitor
Data Source
AI summary
A circuit configured to sense a threshold voltage of an organic light emitting diode (OLED) of a display panel includes a sample and hold unit configured to receive the threshold voltage of the OLED, a first capacitor configured to sample the threshold voltage of the OLED, a second capacitor configured to charge-share the voltage on the first capacitor, an output terminal configured to output the voltage on the second capacitor, and an amplifier including an input terminal connected to the output terminal of the sample and hold unit. The sample and hold unit includes a first switching unit configured to selectively connect the OLED, the first capacitor, the second capacitor, the first capacitor and a first or second reference voltage, the second capacitor and the second or a third reference voltage, and the second capacitor and the output terminal.