Pixel Sensing Device With Three-Staged Operational Amplifier
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Solution Overview
Problem
In organic light emitting display devices, the reduction in pixel current sensing accuracy due to increased leakage current and capacitance variation across the panel poses challenges in accurately compensating for the driving characteristics of OLEDs and TFTs, especially with advancements in high-resolution and high-definition displays.
Innovation Solution
The implementation of a pixel sensing device with a three-staged operational amplifier configuration, including a pre-amplifying unit and two gain amplifying units, increases the input impedance of the operational amplifier, reducing leakage current and enhancing the sensing performance by accurately measuring pixel currents and compensating for capacitance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitance of the feedback capacitor is reduced to sense fine pixel currents, then the sensing precision is improved, but the impedance of the feedback capacitor increases causing increased leakage current into the operational amplifier
Solution Approach 1:
The patent changes the electrical parameters of the operational amplifier by introducing a multi-stage configuration with different gain stages. The first stage has low gain to maintain high input impedance, while subsequent stages provide high overall gain. This parameter change allows the feedback capacitor to maintain low capacitance for fine current sensing without suffering from excessive leakage current, as the high input impedance prevents current loss at the first stage.
Solution Approach 2:
The operational amplifier is segmented into multiple stages: a first operational amplifier stage with low gain and high input impedance for receiving the pixel current signal, and second and third stages with high gain for amplifying the signal. This segmentation allows each stage to perform its specific function optimally - the first stage maintains signal integrity by preventing leakage, while the later stages provide the necessary amplification for precise measurement.
2Measurement precision
If the input impedance of the operational amplifier is increased to reduce leakage current, then the sensing accuracy is improved, but the device complexity increases due to multi-stage configuration
Solution Approach 1:
The operational amplifier is divided into multiple functional stages, each with specific gain characteristics. The first stage handles input signal reception with high impedance requirements, while subsequent stages handle signal amplification. This segmentation resolves the contradiction by distributing the functional requirements across stages rather than requiring a single complex amplifier design.
Solution Approach 2:
The multi-stage operational amplifier configuration serves multiple functions simultaneously: the first stage provides high input impedance for accurate current sensing, while the combined stages provide high overall gain for signal amplification. This multi-functionality approach allows a single integrated circuit to perform both impedance matching and signal amplification tasks that would otherwise require separate components.
3Measurement precision
If the capacitance of the feedback capacitor is made small to maintain constant sensing voltage, then the sensing performance is improved, but the impedance becomes comparable to input impedance causing increased leakage current
Solution Approach 1:
The patent changes the gain parameters of the operational amplifier stages to compensate for the high impedance effect of the small feedback capacitor. By providing high gain in the second and third stages, the system maintains accurate sensing performance with small capacitor values without suffering from leakage current issues, as the high input impedance of the first stage prevents current loss.
Solution Approach 2:
The feedback capacitor is configured to provide negative feedback from the output to the inverting input of the first operational amplifier stage. This feedback mechanism, combined with the multi-stage amplification, ensures that the sensing voltage remains stable and accurate even with small capacitor values, while the high input impedance prevents leakage from compromising the feedback accuracy.
Data Source
AI summary
A pixel sensing device, an organic light emitting display device and a pixel compensation method thereof are disclosed. The pixel sensing device comprises a plurality of current integrators for sensing driving characteristics of pixels. Each current integrator comprises: an operational amplifier equipped with an inverting input terminal to which a first input voltage is applied according to a pixel current of the pixels, a non-inverting input terminal to which a second input voltage is applied according to the pixel current, and an output terminal through which an integral voltage corresponding to the pixel current is output; and a feedback capacitor connected between the inverting input terminal and the output terminal. The operational amplifier comprises: a pre-amplifying unit for lowering an amplifier input gain and being equipped with the inverting and non-inverting input terminals; and two gain amplifying units for receiving an output of the pre-amplifying unit and for making an amplifier output gain higher than the amplifier input gain.