AMOLED Pixel Driving Circuit with Current Mirror Segmentation
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Solution Overview
Problem
The existing AMOLED panels face slow charging times due to small charging currents, especially under low gray levels, which is not suitable for high resolution and high refresh frequency displays.
Innovation Solution
A pixel unit driving circuit and method utilizing a current mirror structure and voltage-dividing circuit to achieve a large ratio between the charging current Idata and the current Ioled flowing through the OLED, ensuring Ioled is within the operation current range while allowing Idata to be a large current, thereby speeding up the charging to the storage capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small charging current Idata is used to charge the storage capacitor Cst, then the OLED current Ioled remains within the operation current range, but the charging speed becomes slow and charging time becomes long
Solution Approach 1:
The charging current path is segmented into two separate paths: one path charges the storage capacitor Cst through the driving TFT T1, while another path provides the OLED driving current through the current mirror TFT T2 and voltage-dividing TFT T3. This segmentation allows independent optimization of charging speed and OLED current control.
Solution Approach 2:
The current mirror TFT T2 and voltage-dividing TFT T3 act as intermediaries between the charging current source and the OLED. The current mirror structure copies and scales the charging current, while the voltage-dividing TFT adjusts the current level, ensuring the OLED receives appropriate current within its operation range even when the charging current is large.
2Speed
If a large charging current Idata is used to speed up charging, then the charging speed increases, but the OLED current Ioled may exceed the operation current range
Solution Approach 1:
The circuit changes the current parameter through the current mirror ratio and voltage-dividing TFT characteristics. By adjusting the width-to-length ratios of the TFTs, the circuit transforms a large charging current into a scaled-down OLED driving current, maintaining the OLED current within operational limits while allowing fast charging with large Idata.
3Quantity of substance
If the storage capacitor Cst has a large capacitance to store sufficient charge, then the charge storage capacity increases, but the charging time becomes especially long under low gray level
Solution Approach 1:
The circuit dynamically adjusts the charging current magnitude based on the required gray level. During the charging phase, the switching unit enables a large charging current to quickly charge the capacitor regardless of the target gray level, eliminating the time loss associated with charging large capacitance values while maintaining the ability to store sufficient charge.
Data Source
AI summary
The present disclosure discloses a pixel unit driving circuit and method, and a pixel unit of an Active Matrix Organic Light Emitting Diode AMOLED panel and a display apparatus. The pixel unit driving circuit of the AMOLED panel comprises: a switching unit, a first input terminal of which is connected to a current source for providing a charging current, a second input terminal of which is connected to an Organic Light-Emitting Diode, and an output terminal of which is connected to a first terminal of a storage capacitor to provide the charging current; the storage capacitor, a first terminal of which is connected to the output terminal of the switching unit, and a second terminal of which is connected to a low level; a driving Thin Film Transistor and a current mirror Thin Film Transistor, gates of which are connected to the first terminal of the storage capacitor, and sources of which are connected to the low level; a voltage-dividing Thin Film Transistor, gate of which is connected to the first terminal of the storage capacitor, a source of which is connected to a drain of the driving Thin Film Transistor, and a drain of which is connected to the Organic Light-Emitting Diode.