Shift Register Output Voltage Control for LCD
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Solution Overview
Problem
Conventional shift registers in LCDs suffer from voltage distortion and incorrect operation due to large transistor sizes and inadequate feedback timing, leading to simultaneous activation of transistors on adjacent data or gate lines, causing display errors.
Innovation Solution
A shift register design utilizing fewer transistors with a specific configuration of switch units and clock signals to control output voltage, including a first switch unit coupled to a clock and signal input, a second switch unit coupled to a clock and voltage input, a third switch unit between clock and output, and a fifth switch unit between output and voltage, allowing for independent voltage control and reducing the need for feedback signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the fourth, fifth, and sixth transistors are designed with larger channel width to handle large current, then the current handling capability is improved, but the shift register volume increases
Solution Approach 1:
The patent changes the voltage level parameter from conventional low voltage to high voltage operation. By operating at higher voltage levels, the transistors can achieve the required current handling capability with smaller channel widths, thereby reducing the overall shift register volume while maintaining the necessary power handling capacity.
2Device complexity
If the last shift register unit does not receive feedback signal, then the device complexity is reduced, but the output voltage cannot be sufficiently pulled down causing waveform distortion
Solution Approach 1:
The patent segments the voltage control function by introducing a dedicated fifth transistor specifically responsible for pulling down the output voltage. This segmentation allows the last shift register unit to independently control its output voltage without relying on feedback signals from subsequent units, eliminating waveform distortion while maintaining simple device architecture.
Solution Approach 2:
The fifth transistor performs the voltage pulling down action in advance and independently, before the next shift register unit operates. This preliminary action ensures that the output voltage is properly discharged without waiting for feedback signals, preventing timing conflicts and waveform distortion.
3Speed
If adjacent shift register units output the same voltage at the same time, then the circuit operation speed is improved, but transistors on adjacent data lines are simultaneously turned on causing incorrect LCD operation
Solution Approach 1:
The fifth transistor in each shift register unit performs preliminary voltage pulling down action independently and in advance, ensuring that each unit completes its voltage discharge before the next unit begins its operation. This eliminates simultaneous voltage output conflicts while maintaining high-speed operation, preventing incorrect LCD behavior.
Data Source
AI summary
An exemplary shift register (20) includes a plurality of shift register units (200) connected one by one. Each of the shift register units includes a first switch unit (201), a second switch unit (202), a third switch unit (203), a fourth switch unit (204), and a fifth switch unit (205). A signal input terminal of each shift register unit is coupled to an output terminal of a rear-stage shift register unit. A first clock input terminal receives a first clock signal to turn on/off the first and second switch units. The third switch unit receives a second clock signal. The fourth switch unit pulls up the output voltage of the output terminal according to a controlling signal from the first switch unit. The fifth switch unit pulls down the output voltage of the output terminal according to controlling signals from the second and third switch units.