Auxiliary Capacitance Driving for High Voltage LCDs
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Solution Overview
Problem
Conventional liquid crystal display devices face challenges in generating sufficient cell voltages beyond the output limits of driver LSIs, especially for new modes like vertical alignment or transverse field modes that require voltages exceeding 5 volts, without complex and costly circuit modifications.
Innovation Solution
A liquid crystal display device and driving method that utilize an auxiliary capacitance line driving circuit to apply different voltages during selection and holding periods, effectively increasing the potential difference between pixel and counter electrodes, allowing for higher voltages across liquid crystal cells without exceeding driver LSI voltage limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the driver LSI output voltage is increased to generate higher cell voltages for new liquid crystal modes, then the voltage requirement is met, but the LSI breakdown voltage limit is exceeded and area/cost increase significantly
Solution Approach 1:
The voltage generation function is segmented between the driver LSI and the auxiliary capacitance circuit. The driver LSI provides base voltages within its safe operating range, while the auxiliary capacitance circuit segments the additional voltage generation task, allowing the LSI to remain within its breakdown voltage limits while still achieving high cell voltages.
Solution Approach 2:
The auxiliary capacitance electrode acts as an intermediary element that stores and releases voltage. It mediates between the driver LSI output and the liquid crystal cell, enabling voltage amplification without requiring the LSI to directly output high voltages, thus avoiding breakdown voltage issues.
2Stress or pressure
If a separate auxiliary capacitance line driving circuit is added to increase voltage, then higher cell voltages are achieved, but the circuit complexity increases
Solution Approach 1:
The auxiliary capacitance line driving circuit is merged with the existing driver LSI structure. The auxiliary capacitance electrodes are integrated into the pixel structure, and the driving signals are combined with the existing scanning and signal line driving schemes, reducing the need for completely separate circuitry.
Solution Approach 2:
The auxiliary capacitance circuit serves multiple functions: it acts as a voltage amplifier, a holding capacitor during the non-selection period, and an AC drive signal generator. This multi-functionality reduces the need for additional dedicated circuits for each function.
3Ease of operation
If the auxiliary capacitance electrode is connected to the counter electrode, then the potential follows the counter electrode, but the voltage across the liquid crystal cannot be increased beyond driver LSI limits
Solution Approach 1:
The connection between the auxiliary capacitance electrode and the counter electrode is made dynamic rather than static. During the selection period, the auxiliary capacitance electrode is connected to the counter electrode for easy potential control. During the non-selection period, the connection is changed to allow voltage accumulation, enabling voltage increase beyond driver LSI limits while maintaining ease of operation during critical periods.
Solution Approach 2:
The auxiliary capacitance electrode undergoes periodic switching between different connection states. It is periodically connected to the counter electrode during selection periods and disconnected or connected to different potentials during non-selection periods, creating a periodic voltage accumulation effect that increases the cell voltage while maintaining control.
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 approach enables the generation of higher voltages across liquid crystal cells, enhancing display performance while maintaining a simple and cost-effective circuit structure, suitable for various liquid crystal display modes.
Implementation Method 1
an auxiliary capacitance whose one end is connected to an output end of each of the switching elements
Data Source
AI summary
A liquid crystal display device is disclosed comprising a display part, a scanning line driving circuit, a signal line driving circuit, a counter electrode driving circuit for providing counter electrodes with a counter electrode driving signal reversed in phase from a signal line driving circuit, an auxiliary capacitance having one end connected to an output end of each of switching elements, and an auxiliary capacitance line driving circuit for driving a plurality of auxiliary capacitance lines arranged in rows and has ends of such auxiliary capacitances in each row commonly connected thereto, wherein the auxiliary capacitance line driving circuit is adapted to apply a first voltage to the auxiliary capacitance lines for a first half cycle of the counter electrode driving signal and apply a second voltage thereto for a (p+½)th cycle after the first period of the counter electrode driving signal where p is 0 or a natural number, said auxiliary capacitance line driving circuit making the auxiliary capacitance line in a floating condition after said (p+½) th cycle during the remaining holding time.