OLED Sensing Circuit Noise Reduction via Differential Amplification
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Solution Overview
Problem
Existing organic light emitting display devices face challenges in achieving desired image quality due to luminance deviations caused by variations in the electrical characteristics of driving TFTs, with external compensation methods being time-consuming and internal methods complicating pixel structure and reducing aperture ratio, while current sensing units occupy large areas and introduce noise.
Innovation Solution
A sensing unit circuit is designed with a fully differential amplifier, integrator, sampling unit, and analog-to-digital converter, utilizing switches and capacitors to differentially amplify currents from adjacent sensing lines, reducing noise and area by half, and allowing operation mode switching between CDS and general modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external compensation method is used to sense driving TFT characteristics, then luminance deviation can be compensated, but the sensing process takes much time
Solution Approach 1:
The patent merges the sensing function with the pixel structure by integrating the sensing unit directly into the pixel, combining data writing and characteristic sensing operations. This allows simultaneous or overlapping execution of display and sensing tasks, significantly reducing the time loss associated with separate external sensing operations.
2Measurement precision
If an internal compensation method is used to compensate luminance deviation in real time, then luminance deviation can be compensated, but the pixel structure becomes complex and aperture ratio decreases
Solution Approach 1:
The sensing unit is designed to perform multiple functions: it senses driving TFT characteristics, generates sensing signals, and interfaces with both display data writing and compensation operations. This multi-functionality reduces the need for separate dedicated circuits, thereby limiting the increase in pixel structure complexity while maintaining real-time compensation capability.
3Measurement precision
If a sensing unit with OP Amp and scaler per sensing line is used, then driving TFT characteristics can be sensed, but the sensing unit occupies a large area
Solution Approach 1:
The patent merges adjacent sensing lines to share common sensing units, combining the functionality of multiple OP Amps and scalers into shared resources. This reduces the total sensing unit area while maintaining the precision of driving TFT characteristic sensing through the integrated fully differential amplifier architecture.
4Measurement precision
If current sensing is performed through sensing lines, then driving TFT characteristics can be detected, but noise influences the sensing accuracy
Solution Approach 1:
The patent converts the harmful noise effect into a benefit by using fully differential sensing that deliberately introduces correlated noise paths. The differential amplifier architecture subtracts common-mode noise signals while preserving the differential sensing signal, effectively converting noise that affects both paths equally into a cancelable common-mode component.
Data Source
AI summary
An organic light emitting display device in an embodiment of the present invention comprises a display panel equipped with a plurality of pixels each including an OLED and a driving TFT for driving the OLED and a sensing circuit connected to pixels through a sensing line and detecting driving characteristics of a corresponding pixel. The sensing circuit may comprise a plural sensing units including an integrator for integrating currents respectively flowing two adjacent sensing lines connected to inverting and non-inverting input terminals of a fully differential amplifier, a sampling unit for respectively sampling two integral outputs of the integrator and a scaler for regulating an operating range of outputs of the sampling unit, a differential amplifier for differentially amplifying one or more outputs of the scaler, and an ADC for converting an output of the differential amplifier into a digital sensing value.