AMOLED Pixel Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The prior art pixel driving circuits in Active Matrix OLED displays face issues with non-uniformity in threshold voltages due to process limitations and temperature effects, leading to inconsistencies in display brightness across different pixel units.
Innovation Solution
A pixel driving circuit with a charging compensation module and a light-emitting control module, which includes specific transistors and capacitors to compensate for threshold voltage variations, ensuring consistent over-driving voltages and uniform light emission across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a common pixel driving circuit structure with driving transistor M1 and switch transistor M2 is used, then the OLED can be driven in active matrix manner with constant current control, but the threshold voltages of driving transistors become non-uniform due to process limitations and temperature shifts, resulting in non-uniform display brightness
Solution Approach 1:
The patent applies preliminary action by introducing a compensation transistor M3 and capacitor C1 that pre-compensate for threshold voltage variations before the main driving transistor M1 operates. The compensation circuit stores the threshold voltage information in capacitor C1 during a compensation phase, then uses this stored information to adjust the driving voltage, thereby eliminating the non-uniformity caused by process limitations and temperature shifts before they affect display brightness
Solution Approach 2:
The patent implements feedback by using the compensation transistor M3 to sense and store the actual threshold voltage of the driving transistor M1 in capacitor C1. This stored threshold voltage information is then fed back to adjust the gate voltage of M1, creating a closed-loop system that continuously compensates for threshold voltage variations, thereby maintaining uniform display brightness across all pixels
2Manufacturing precision
If the over-driving voltage is increased to compensate for threshold voltage variations, then the display brightness uniformity improves, but the OLED lifespan decreases due to increased stress and aging effects
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the gate voltage of the driving transistor M1 based on the stored threshold voltage information in capacitor C1. Instead of using a fixed high over-driving voltage that stresses the OLED, the circuit precisely modulates the driving parameters to match each pixel's actual threshold voltage, achieving uniform brightness while operating the OLED within safe voltage limits that preserve its lifespan
Data Source
AI summary
A pixel driving circuit, an array substrate and a display apparatus, the pixel driving circuit includes a driving transistor and an organic light-emitting diode, it further comprises: a charging compensation module, for receiving a data voltage signal, charging the driving transistor and compensating for a threshold voltage of the driving transistor, under the control of a scan voltage signal; and a light-emitting control module, for receiving a reference voltage and a power supply voltage, and controlling the organic light-emitting diode to emit lights, under the control of a light-emitting control signal. The problem of the non-uniformity of threshold voltages is eliminated by compensating for the threshold voltages of driving transistors thereby enhancing the display effect of the display apparatus.