AMOLED Pixel Driving Circuit Threshold Voltage Drift Compensation
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Solution Overview
Problem
The existing AMOLED pixel driving circuits, such as the 2T1C and 6T1C structures, face issues with threshold voltage drift of driving TFTs and voltage drops in the positive power supply, leading to uneven brightness and display defects due to their dependence on threshold voltage and power supply voltage, which affect the driving current and image quality.
Innovation Solution
A 6T1C AMOLED pixel driving circuit is designed with a specific configuration of TFTs and a storage capacitor, where the driving current is made independent of the threshold voltage and positive power voltage by utilizing a reset, compensation, and light-emitting phase control using scan and light-emitting control signals, allowing for effective compensation of threshold voltage drift and voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple 2T1C AMOLED pixel driving circuit is used, then the device complexity is reduced, but the threshold voltage drift of the driving TFT causes driving current changes and uneven brightness
Solution Approach 1:
The pixel driving circuit is divided into multiple functional modules: a driving TFT for current control, a compensation TFT for threshold voltage compensation, and a storage capacitor for voltage holding. This segmentation allows each component to perform its specific function independently, resolving the contradiction between circuit simplicity and display quality by adding only the necessary compensation functionality.
Solution Approach 2:
The compensation TFT performs threshold voltage compensation in advance during the compensation phase before the light-emitting phase. By pre-compensating the threshold voltage drift, the circuit ensures stable driving current throughout the display period without requiring continuous complex control, thus improving reliability while maintaining reasonable complexity.
2Reliability
If a conventional 6T1C AMOLED pixel driving circuit is used, then the threshold voltage compensation function is added, but the voltage drop in the positive power supply cannot be compensated
Solution Approach 1:
The storage capacitor is designed to serve multiple functions: it stores the compensated gate voltage for the driving TFT, holds the reference voltage for compensation, and adapts to power supply voltage variations. This multi-functionality allows the circuit to handle both threshold voltage drift and power supply voltage drops without requiring additional dedicated components, thus improving adaptability while maintaining circuit simplicity.
Solution Approach 2:
The compensation mechanism uses feedback from the actual circuit operating conditions to adjust the driving TFT gate voltage. By monitoring the threshold voltage drift and power supply variations, the compensation TFT dynamically adjusts the gate voltage to maintain stable driving current, enabling the circuit to adapt to different power supply conditions while providing threshold voltage compensation.
3Device complexity
If the driving current depends on the threshold voltage of the driving TFT, then the circuit design is simplified, but the threshold voltage drift causes driving current changes and display defects
Solution Approach 1:
The compensation TFT creates a copy of the threshold voltage effect by measuring the voltage drop across a test capacitor that experiences the same threshold voltage drift as the driving TFT. By copying and measuring this effect separately, the circuit can calculate and compensate for the threshold voltage drift without changing the basic driving current generation mechanism, thus maintaining design simplicity while improving current stability.
Data Source
AI summary
The invention provides an AMOLED pixel driving circuit, driving method and terminal. The AMOLED pixel driving circuit adopts a 6T1C structure, comprising a first TFT, i.e., driving TFT, a second TFT, a third TFT, a fourth TFT, a fifth TFT, a sixth TFT, a storage capacitor and an OLED; the scan signal, the first light-emitting control signal and the second light-emitting control signal are combined to successively correspond to a reset phase, a compensation phase and a light-emitting phase, so that the driving current flowing through the OLED is independent of the threshold voltage of the driving TFT and the positive power voltage. The invention compensates for the threshold voltage drift of the driving TFT and also for the voltage drop in positive power voltage.