Voltage-Current Conversion Circuit for Display Uniformity
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Solution Overview
Problem
Active matrix EL display devices require additional ICs with voltage-current conversion circuits to convert voltage video signals into current signals, increasing production costs and suffering from nonuniformity due to TFT variations.
Innovation Solution
Incorporating a voltage-current conversion circuit with an output transistor and compensation circuit to convert voltage video signals into current signals, eliminating inaccurate output currents and compensating for threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a voltage-current conversion circuit is implemented using an additional IC, then current signals can be supplied to drive pixel circuits, but production costs increase due to separate IC preparation and development
Solution Approach 1:
The voltage-current conversion circuit is merged with the pixel circuit itself by integrating the output transistor and compensation circuit directly into the pixel structure. This eliminates the need for separate ICs and allows current signals to be generated within the display device using the same TFT technology, thereby reducing production costs while maintaining the ability to supply current signals to drive the pixel circuits
Solution Approach 2:
The pixel circuit is designed to perform multiple functions: it serves as both the display element and the voltage-current conversion circuit. The output transistor and compensation circuit within the pixel circuit enable it to convert voltage signals to current signals while simultaneously driving the EL element, eliminating the need for dedicated conversion ICs and reducing overall system complexity
2Ease of operation
If a voltage-current conversion circuit is implemented using an additional IC, then current signals can be supplied to drive pixel circuits, but device complexity increases due to additional components
Solution Approach 1:
The voltage-current conversion functionality is merged into the pixel circuit by integrating the output transistor and compensation circuit directly into the pixel structure. This eliminates the need for separate ICs and reduces the overall number of components in the display device while maintaining the ability to supply current signals to drive the pixel circuits
3Device complexity
If conventional voltage driving is used, then device complexity is reduced, but display uniformity deteriorates due to nonuniformity from TFT variations
Solution Approach 1:
The compensation circuit uses feedback mechanisms to detect and correct threshold voltage variations in the output transistor. By monitoring the actual threshold voltage and adjusting the gate voltage accordingly, the circuit compensates for TFT variations and ensures uniform current output across all pixels, thereby improving display uniformity without significantly increasing device complexity
Solution Approach 2:
The compensation circuit dynamically adjusts the gate voltage parameter of the output transistor to compensate for threshold voltage variations. By changing the gate voltage parameter in response to detected variations, the circuit maintains consistent current output despite TFT manufacturing variations, thereby improving display uniformity
Data Source
AI summary
A video signal line receives a voltage video signal. The supplied voltage video signal is provided to a voltage-current conversion circuit in a corresponding column. The voltage-current conversion circuit converts the voltage video signal into a current signal, and supplies the current signal to a corresponding pixel circuit. Each voltage-current conversion circuit includes an output transistor for supplying current in accordance with the voltage video signal, and a compensation circuit for compensating for variations in threshold of the output transistor.