TFT Compensation Circuit for OLED Displays Using Reference Current
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Solution Overview
Problem
Conventional pixel TFT circuits for OLED displays have limitations in tolerating variations in threshold voltage and carrier mobility, requiring multiple compensation phases and large capacitors, making them unsuitable for high-resolution displays with many pixels.
Innovation Solution
A pixel circuit that applies a constant reference current through the drive transistor during a simultaneous compensation and programming phase, storing voltages related to threshold voltage and carrier mobility on a single storage capacitor, allowing for simultaneous compensation and programming in a single phase, reducing the need for multiple capacitors and shortening the horizontal time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional compensation circuits are used with multiple capacitors and phases, then threshold voltage and carrier mobility variations are compensated, but the compensation time is long and the pixel area is large
Solution Approach 1:
The patent combines threshold voltage compensation and carrier mobility compensation into a single simultaneous phase. The drive transistor is configured to receive both reference current (for threshold voltage compensation) and data voltage (for carrier mobility compensation) at the same time, eliminating the need for separate compensation phases required by conventional circuits.
Solution Approach 2:
The patent extracts the compensation function from multi-phase operations and consolidates it into a single phase by selectively configuring the drive transistor to perform both compensation tasks simultaneously, reducing the time required while maintaining compensation effectiveness.
2Reliability
If conventional compensation circuits with multiple capacitors are used, then compensation is achieved, but the pixel area increases
Solution Approach 1:
The patent merges the functions of multiple capacitors into a single storage capacitor. By configuring the drive transistor to be diode-connected during compensation, the circuit stores both threshold voltage compensation information and carrier mobility compensation information in one capacitor, reducing the total area required.
Solution Approach 2:
The single storage capacitor performs multiple functions: storing threshold voltage compensation voltage and storing carrier mobility compensation voltage, effectively replacing what would traditionally require multiple specialized capacitors in conventional circuits.
3Productivity
If reference current is applied through drive transistor simultaneously with data voltage, then both compensations occur in one phase, but circuit configuration must be specific
Solution Approach 1:
The patent uses dynamic configuration of the drive transistor, switching between diode-connected mode during compensation and normal transistor mode during emission. This dynamic reconfiguration allows the same transistor to serve different functions at different times, achieving fast simultaneous compensation without requiring entirely separate circuit paths.
Data Source
AI summary
A pixel circuit for a display device includes a drive transistor configured to control an amount of current to a light-emitting device during an emission phase depending upon a voltage applied to a gate of the drive transistor; a second transistor connected to the gate of the drive transistor, wherein the second transistor is in an on state during a combined programming and compensation phase and in an off state during the emission phase, and when the second transistor is in an on state the drive transistor becomes diode-connected such that a gate and a second terminal of the drive transistor are connected through the second transistor; a third transistor connected to the second terminal of the drive transistor, wherein the third transistor is in an on state during the combined programming and compensation phase to permit a reference current to be applied through the drive transistor, and is in an off state during the emission phase to remove the reference current; and a capacitor having a first plate that is connected to the gate of the drive transistor and a second plate that is connectable to a data voltage during the combined programming and compensation phase. A threshold voltage and/or a carrier mobility of the drive transistor is compensated by application of the reference current during the combined programming and compensation phase.