Current Sensing Device for OLED Noise Reduction
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Solution Overview
Problem
Current sensing technologies in organic light-emitting display devices are vulnerable to noise amplification due to parasitic capacitance, which distorts the sensing results for pixel currents, making it difficult to accurately sense and compensate for the driving characteristics of OLEDs and TFTs.
Innovation Solution
A current sensing device with a current transmitting unit that separates the electric connection between the sensing line and the current integrator, using mirroring transistors to mirror the pixel current and output a greater mirrored current, and a current buffer to maintain a constant source node voltage, thereby reducing noise amplification and improving sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the feedback capacitor capacitance is made small to reduce sensing time and maintain constant output voltage, then sensing speed is improved, but noise amplification increases due to parasitic capacitance of sensing lines
Solution Approach 1:
The patent introduces a current transmitting unit as an intermediary component between the sensing line and the current integrator. This unit includes a buffer amplifier and mirroring transistors that transfer the pixel current to the integrator without directly connecting the sensing line to the integrator input. By doing so, the parasitic capacitance of the sensing line is isolated from the integrator's feedback capacitor, preventing noise amplification while allowing the use of smaller feedback capacitors for faster sensing.
2Object-affected harmful factors
If the feedback capacitor capacitance is increased to reduce noise amplification, then noise resistance is improved, but sensing time increases and output voltage becomes non-constant
Solution Approach 1:
The patent segments the sensing system into distinct functional blocks: a sensing line, a current transmitting unit with buffer amplifier, and a current integrator with feedback capacitor. This segmentation allows the feedback capacitor to be optimized for noise resistance (larger capacitance) without directly affecting the sensing line's parasitic capacitance, as the current transmitting unit acts as an isolation barrier. The buffer amplifier maintains constant output voltage while the integrator integrates current over the sensing period.
3Device complexity
If the sensing line is directly connected to the current integrator to simplify the circuit, then device complexity is reduced, but noise from reference voltage variation and sensing line parasitic capacitance distorts the sensing result
Solution Approach 1:
The current transmitting unit serves as an intermediary that isolates the current integrator from noise sources in the sensing line. The buffer amplifier within this unit has high input impedance that matches the sensing line characteristics, and its output drives the integrator's inverting input terminal. This intermediate stage prevents reference voltage noise and sensing line parasitic capacitance from directly affecting the integrator's feedback capacitor, thereby maintaining sensing accuracy without excessive circuit complexity.
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 effectively minimizes noise distortion in sensing results, allowing for accurate sensing and compensation of pixel currents, even with low current levels, and enables the use of larger feedback capacitors in current integrators, enhancing the reliability of driving characteristic measurements.
Implementation Method 1
a feedback capacitor connected between the inverting input terminal and the output terminal
Implementation Method 2
a current transmitting unit connected between the sensing line and the current integrator to separate the electric connection of the sensing line and the current integrator, wherein the current transmitting unit mirrors the pixel current and causes the mirrored current to be output from the inverting input terminal
Data Source
AI summary
A current sensing device and the organic light-emitting display device including the same are disclosed. The current sensing device may include a plurality of sensing units, each sensing unit playing a role of converting a pixel current input through a sensing line into a digital sensing value, and each sensing unit comprising: a current integrator including an integrating amplifier and a feedback capacitor, the integrating amplifier comprising an inverting input terminal, a non-inverting input terminal and an output terminal, wherein the feedback capacitor is connected between the inverting input terminal and the output terminal, and a first reference voltage is input to the non-inverting input terminal; and a current transmitting unit connected between the sensing line and the current integrator to separate the electric connection of the sensing line and the current integrator, wherein the current transmitting unit mirrors the pixel current and causes the mirrored current to be output from the inverting input terminal of the integrating amplifier.