Demultiplexer Driving Circuit for Reducing Display Frame Size
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Solution Overview
Problem
In high-definition display systems, the connection pitches for data lines become too small, making it difficult to connect X drivers to data lines, leading to a large frame size due to the need for large transistors with low ON resistance, especially when using amorphous silicon type thin film transistors with low mobility.
Innovation Solution
A driving circuit that divides data lines into groups and uses first and second transistors, along with operational amplifiers and control circuits to manage voltage levels and ON resistance, allowing correct data signal supply even with high ON resistance, thereby reducing the frame size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If data lines are divided into groups and a demultiplexer is used to sequentially select data lines, then the number of input terminals of the demultiplexer decreases and connection pitches are loosened, but large transistors are required to decrease ON resistance, causing the frame size to become large
Solution Approach 1:
The data lines are divided into multiple groups (e.g., three groups), and a demultiplexer sequentially selects one data line from each group at a time. This segmentation reduces the number of input terminals of the demultiplexer to 1/3 of the total data lines, thereby loosening the connection pitches and enabling easier mounting of X drivers in the display panel.
Solution Approach 2:
The patent changes the electrical parameters by introducing operational amplifiers that actively control the voltage at the source terminal of the first transistor. This allows the system to use transistors with higher ON resistance (smaller transistors) while maintaining correct data signal supply, thereby reducing the frame size without compromising manufacturing ease.
2Reliability
If amorphous silicon type thin film transistors with low mobility are used, then large transistors are required to achieve low ON resistance, but large transistors increase the frame size
Solution Approach 1:
The patent introduces operational amplifiers that provide negative feedback control. The operational amplifiers detect the voltage at the source terminal of the first transistor and adjust the gate voltage accordingly to maintain the correct data signal voltage level. This feedback mechanism compensates for the high ON resistance of small transistors, allowing the use of smaller transistors with lower mobility materials like amorphous silicon without compromising signal integrity, thus reducing frame size while maintaining reliability.
Solution Approach 2:
The operational amplifier acts as an intermediary between the data signal output circuit and the data line. It buffers and regulates the voltage, ensuring that the data signal is correctly supplied to the data line even when the first transistor has high ON resistance. This intermediary component enables the use of smaller transistors without sacrificing signal quality.
3Quantity of substance
If the number of data lines is increased for high-definition display, then the number of pixels increases, but the connection pitches become too small to connect X drivers
Solution Approach 1:
The patent segments the large number of data lines into multiple groups (e.g., three groups). The demultiplexer sequentially selects one data line from each group, reducing the number of simultaneous connections required at any one point. This segmentation enables high-definition displays with many pixels while maintaining manageable connection pitches that are feasible for manufacturing.
Solution Approach 2:
The demultiplexer operates by periodically selecting data lines in a sequential manner, cycling through the groups of data lines over time. This periodic action allows a single set of X drivers to serve multiple data line groups over time, reducing the immediate connection requirements and enabling high-definition displays with finer pitch requirements.
Data Source
AI summary
The object of the present invention is to decrease a frame size in a case where data lines are driven by using a demultiplexer. The data lines 114 are divided into groups each having three data lines. TFTs 52 and 54 are provided for each data line 114, and the TFT 52 between the TFTs has a source electrode commonly connected in each group and a drain electrode connected to the data line 114. In addition, the TFT 54 has a source electrode connected to the data line 114 and a drain electrode commonly connected in each group. A data signal output circuit 32 that outputs data signals having voltage values in accordance with gray scale levels of sub-pixels corresponding to intersections of a selected scan line and a selected data line in each group to each group. Since the selected data line 114 is connected to an inverting input terminal of an operational amplifier 34 through the TFT 54, the operational amplifier 34 controls the voltage of the data line 114 to be identical to the voltage of a signal output from the data signal output circuit.