Pixel Circuit Source Follower Threshold Voltage Correction
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Solution Overview
Problem
Existing self-light-emitting display apparatuses face challenges in accurately controlling current flow to light emitting elements, leading to variations in threshold voltage and increased power consumption, particularly in high-resolution displays, due to issues with polysilicon TFTs and the need for multiple capacitors and power source line control switches.
Innovation Solution
A pixel circuit with a source follower type connection that uses a capacitor connected to the gate of a driving transistor, switching transistors to control voltage differences, and a reference voltage line to correct threshold voltage variations while maintaining a constant power source voltage, reducing power consumption and eliminating the need for multiple capacitors and power source line control switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If polysilicon TFT is used for driving transistor to achieve high field effect mobility and high ON current, then the display apparatus can achieve high resolution, but variation in threshold voltage occurs due to lattice defects on crystalline grain boundaries
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to a voltage higher than the power source voltage before the actual display operation. This pre-charge voltage compensates for the threshold voltage variations that will occur during operation, ensuring stable display performance without requiring multiple capacitors or power source line control switches.
2Reliability
If the potential of the power source line is changed to correct threshold variation, then threshold voltage correction is achieved, but power consumption increases due to high parasitic capacitance of wide wiring and additional power source line control switches are required
Solution Approach 1:
The patent extracts the threshold voltage correction function from the power source line control system and relocates it to a local capacitor-based compensation circuit within each pixel. This eliminates the need for power source line potential changes and associated control switches, thereby reducing power consumption while maintaining correction effectiveness.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element that stores and releases voltage to compensate for threshold variations. This capacitor acts as a local energy reservoir, eliminating the need to change power source line potentials and reducing the parasitic capacitance and power consumption associated with wide wiring and control switches.
3Reliability
If a pre-charge voltage higher than the power source voltage is applied to correct threshold variation without changing power source line, then threshold correction is achieved, but the required voltage range increases and power consumption increases
Solution Approach 1:
The patent applies dynamics by making the capacitor voltage dynamic - it is charged to a higher voltage temporarily during pre-charge, then discharged to provide compensation during operation. This dynamic voltage adjustment allows threshold correction without permanently increasing the voltage range or power consumption.
4Reliability
If multiple capacitors are used in the pixel circuit to correct threshold variation, then threshold correction is achieved, but it becomes difficult to achieve high resolution due to increased device complexity
Solution Approach 1:
The patent makes the single capacitor multi-functional by using it for both pre-charge and threshold voltage compensation. This universal approach eliminates the need for multiple dedicated capacitors, reducing device complexity while maintaining high resolution capability.
Data Source
AI summary
A pixel circuit with a source follower type connection is provided that corrects variation in threshold voltage of a driving transistor, reduces power consumption and realizes high resolution. The pixel circuit includes: a data line for supplying a data voltage; a power source line for supplying a power source voltage; a reference voltage line for supplying a reference voltage lower than the power source voltage; a plurality of control signal lines for supplying control signals; a light emitting element; a driving transistor; a capacitor; and a plurality of switching transistors. The circuit writes the data voltage through one end of the capacitor and subsequently connects the one end of the capacitor to the anode electrode of the light emitting element.