Level Shift Circuit for Display Drive Voltage Conversion
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Solution Overview
Problem
In drive-circuit integral type display devices, poly-silicon transistors exhibit high and irregular threshold values, making it difficult to operate the drive circuit with a level shift circuit, especially when input signals have voltage levels that are lower or higher than the threshold value, leading to inefficiencies in voltage conversion and increased power consumption.
Innovation Solution
The implementation of a level shift circuit with a transistor and connected resistance, where the transistor is brought into an ON state by a gate voltage, and an input signal is applied to the source terminal, allowing for voltage level conversion by adjusting the drain resistance to manage voltage drops and outputs, and using multiple level shift circuits with varying drain resistances to account for threshold value irregularities, along with an exclusive-OR circuit to select the correctly operating circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a level shift circuit is used to convert voltage levels in a drive-circuit integral type display device, then voltage level conversion is achieved, but the circuit cannot be operated properly when using poly-silicon transistors due to high and irregular threshold values
Solution Approach 1:
The invention changes the material parameter of the transistor from poly-silicon to single-crystal silicon, which fundamentally alters the threshold value characteristics. Single-crystal silicon transistors exhibit lower and more uniform threshold values compared to poly-silicon, enabling reliable level shift circuit operation while maintaining voltage level conversion capability
Solution Approach 2:
The invention uses a transistor with different material properties (single-crystal silicon instead of poly-silicon) to replicate the desired function of voltage level conversion while avoiding the threshold value irregularities inherent in poly-silicon transistors
2Area of stationary object
If poly-silicon transistors are used in the drive circuit, then the display device can be miniaturized with integrated circuits, but the threshold values are high and irregular making circuit operation difficult
Solution Approach 1:
The invention changes the material composition parameter of the transistor from poly-silicon to single-crystal silicon, which results in more uniform and predictable threshold values. This material substitution maintains the miniaturization benefit of integrated circuits while resolving the threshold value irregularity problem
3Adaptability or versatility
If the transistor is kept in ON state to allow input signal passage, then voltage level conversion works for low voltage levels, but power consumption increases and high voltage levels equal to or below threshold cannot be properly handled
Solution Approach 1:
The invention makes the transistor operation dynamic by using a gate voltage to control the ON/OFF state. The transistor is turned ON during the period when input signals are present to enable voltage level conversion, and turned OFF when no input signals are present to reduce power consumption, thus adapting to different operational conditions
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 effective voltage level conversion, even with high or low input signal levels, reduces power consumption, and enhances circuit design flexibility by adjusting drain resistances and using multiple level shift circuits to compensate for threshold value fluctuations, ensuring optimal operation of the drive circuit.
Implementation Method 1
the transistor assumes an ON state so as to input an input signal to a source terminal and the input signal assumes a low voltage level, a drain terminal assumes a low voltage level, whereby even when the input signal assumes a high voltage level equal to or lower than a threshold value, a drain terminal outputs a voltage equal to or more than the threshold value as a high voltage level
Implementation Method 2
a resistance is connected to a drain terminal of the transistor to supply a voltage to the drain terminal through the resistance
Data Source
AI summary
In the display device which is used in a miniaturized portable equipment, when a drive circuit is also connected on the same substrate as pixels, an input signal of low voltage has a level thereof shifted even when the threshold value is large or fluctuated. The display device includes pixel electrodes, switching elements which supply video signals to the pixel electrodes, and a drive circuit which supplies the video signals to the switching elements on the same substrate, wherein the drive circuit includes a level shift circuit, the level shift circuit includes a transistor. In a state that the transistor assumes an ON state, when an input signal is inputted to a source terminal and the input signal is at a low voltage level, a drain terminal assumes a low voltage level. Further, even when the input signal is at a high voltage level equal to or lower than a threshold value, the drain terminal outputs a voltage equal to or more than the threshold value as a high level voltage.