Scan Line Driver Bootstrap Circuit for Low-Power Display Signals
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Solution Overview
Problem
Existing active matrix display devices face challenges with increased power consumption due to the need for higher amplitude signals and potential signal distortion, particularly in scan line switching elements, which are exacerbated by the higher number of scan and signal lines in high-definition and larger displays.
Innovation Solution
The semiconductor device incorporates a scan line driver circuit with transistors and capacitors to achieve bootstrap operation, ensuring sufficient signal amplitude and reducing distortion while maintaining low power consumption by utilizing light-transmitting conductive layers for the pixel and transistor electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the number of scan lines and signal lines is increased to achieve high definition and larger display size, then the display quality and size are improved, but the power consumption is increased
Solution Approach 1:
The scan line driver circuit is divided into multiple independent driver circuits, each driving a subset of scan lines. This segmentation reduces the number of output terminals required from each individual driver circuit, thereby reducing power consumption while still supporting a large total number of scan lines for high definition displays.
2Device complexity
If conventional scan line switching elements are used, then the circuit structure is simple, but the signal amplitude is reduced by the threshold voltage of the switching element
Solution Approach 1:
A bootstrap capacitor is introduced as an intermediary element between the driver circuit output and the scan line switching element. This capacitor stores voltage and provides it to the switching element, compensating for the threshold voltage drop and ensuring sufficient signal amplitude reaches the scan line without requiring a more complex circuit structure.
3Loss of information
If additional signal amplitude is provided to compensate for threshold voltage loss, then the signal amplitude is sufficient, but the power consumption is increased
Solution Approach 1:
The bootstrap capacitor is pre-charged during a bootstrap period when the scan line switching element is off, storing voltage in advance. This preliminary action ensures that when the switching element turns on, the stored voltage compensates for the threshold voltage drop, providing sufficient signal amplitude without requiring continuous additional power input.
4Reliability
If the scan line switching element duty ratio is reduced to improve reliability, then the reliability is improved, but the power consumption is increased
Solution Approach 1:
The bootstrap capacitor serves multiple functions: it compensates for threshold voltage loss, maintains sufficient signal amplitude, and enables the switching element to operate with a lower duty ratio. By making the capacitor self-charging during the off-period of the switching element, the system achieves improved reliability without additional power consumption penalties.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables efficient signal transmission with adequate amplitude and reduced rising and falling times, minimizing power consumption without the need for higher power supply voltages, thus optimizing display performance.
Implementation Method 1
A semiconductor device is developed that includes a display element with pixels containing transistors, a scan line driver circuit, and a capacitor for holding voltage
Data Source
AI summary
It is an object to provide a semiconductor device which can supply a signal with sufficient amplitude to a scan line while power consumption is kept small. Further, it is an object to provide a semiconductor device which can suppress distortion of a signal supplied to the scan line and shorten a rising time and a falling time while power consumption is kept small. A semiconductor device which includes a plurality of pixels each including a display element and at least one first transistor and a scan line driver circuit supplying a signal for selecting the plurality of pixels to a scan line. A light-transmitting conductive layer is used for a pixel electrode layer of the display element, a gate electrode layer of the first transistor, source and drain electrode layers of the first transistor, and the scan line. The scan line driver circuit includes a second transistor and a capacitor for holding a voltage between a gate electrode layer of the second transistor and a source electrode layer of the second transistor. The source electrode of the second transistor is connected to the scan line.