PWM Pixel Circuit Using N-Type Driving TFTs for High-Resolution Displays
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Solution Overview
Problem
Conventional pixel circuits for ultra-high resolution displays, driven in pulse width modulation with internal threshold voltage compensation, require 19 or more transistors and 3 or more capacitors, limiting their integration and suffering from afterimage, response time, and luminance characteristics degradation due to P-type driving transistors.
Innovation Solution
A pixel circuit design with fewer transistors, including 10 transistors and 2 capacitors, utilizing N-type and P-type transistors, and a novel configuration for internal threshold voltage compensation, enabling integration in ultra-high resolution displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel circuits use 19 or more transistors and 3 or more capacitors for PWM driving with internal threshold voltage compensation, then threshold voltage compensation is achieved, but device area increases and integration becomes difficult for ultra-high resolution displays
Solution Approach 1:
The patent merges the threshold voltage compensation function into the existing pixel circuit structure by utilizing the driving transistor itself and shared voltage terminals. The compensation is achieved through the natural voltage drops across the driving transistor during different operation phases (initialization, data writing, emission), eliminating the need for separate compensation transistors and capacitors. This integration reduces the total component count while maintaining compensation functionality.
Solution Approach 2:
The driving transistor serves multiple functions: it acts as the primary switching element for PWM control, provides threshold voltage compensation through its inherent characteristics, and shares voltage terminals with other circuit functions. The emission voltage terminal and initialization voltage terminal are shared across different transistors, making the circuit elements serve universal purposes rather than dedicated single functions, thereby reducing overall device complexity.
2Ease of manufacture
If P-type transistors are used as driving transistors in PWM pixel circuits, then the circuit structure is established, but afterimage characteristics deteriorate and response time increases
Solution Approach 1:
The patent changes the key parameter of transistor type from P-type to N-type for the driving transistor. This parameter change fundamentally alters the electrical characteristics: N-type transistors exhibit faster switching speeds, lower on-resistance, and better charge carrier mobility, which directly improve response time and reduce afterimage effects. The voltage terminal configurations are adjusted accordingly to match N-type transistor operation characteristics, maintaining proper initialization and emission voltage levels.
Data Source
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AI summary
A pixel circuit includes a first transistor, a second transistor, a third transistor, a seventh transistor, a ninth transistor and a light emitting element. The first transistor includes a control electrode connected to a first node, a first electrode connected to a second node and a second electrode connected to a third node. The second transistor is connected to the first node and the second node. The third transistor is configured to apply a data voltage to the first transistor. The seventh transistor is connected to a fourth node and configured to apply a driving current to the light emitting element. The ninth transistor is configured to apply a constant-current voltage to the fourth node. The light emitting element is configured to emit a light based on the data voltage and the constant-current voltage. The first transistor is an N-type transistor. The seventh transistor is a P-type transistor.