Voltage Level Converter Circuit for Display Devices
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Solution Overview
Problem
Existing liquid crystal display devices face challenges in voltage level conversion due to low output voltage from polycrystalline silicon transistors, leading to insufficient driving voltage and increased through current, especially when the low level of an input signal differs from the low level of an output signal.
Innovation Solution
A voltage level converter circuit is implemented, comprising a charger circuit, a discharge circuit, and a reset signal generating circuit, using MIS TFTs with polycrystalline silicon semiconductor layers, to effectively convert input voltage levels while minimizing through current, even when input and output signal levels differ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a voltage level converter circuit using polycrystalline silicon transistors is used, then the circuit can be formed on the substrate concurrently with pixel formation, but the output voltage is low and insufficient driving voltage is obtained
Solution Approach 1:
A charge pump circuit is introduced as an intermediary voltage boosting device between the low-voltage polycrystalline silicon circuit and the liquid crystal display elements. This charge pump circuit converts the low output voltage from the polycrystalline silicon transistors to a higher voltage level suitable for driving the liquid crystal elements, thereby resolving the voltage insufficiency while maintaining the manufacturing advantage of using polycrystalline silicon circuits formed concurrently with pixels
2Adaptability or versatility
If the low level of input signal differs from the low level of output signal, then voltage level conversion is needed, but through current increases
Solution Approach 1:
The charge pump circuit serves as a mediator that enables voltage level conversion between different low levels without causing excessive through current. By using the charge pump architecture with switching transistors and capacitors, the circuit can adapt to different input and output voltage levels while minimizing direct current paths that would cause energy loss
Solution Approach 2:
The voltage level conversion is achieved through periodic charging and discharging cycles of the charge pump circuit. The switching transistors operate in periodic cycles to transfer charge from the input to the output, enabling voltage level adaptation without maintaining continuous current flow, thereby reducing through current and energy loss
Data Source
AI summary
A voltage level converter for driving resistive and capacitive loads of a display device includes a charge circuit having a capacitance, a transistor NMOS1, a capacitance, and a transistor; a discharge circuit having transistors; and a reset signal generating circuit provided in a preceding stage of the discharge circuit. A signal having an inverted phase to an input pulse is applied to the reset signal generating circuit. An output of the reset signal generating circuit is supplied to gate terminals of the transistors, thus realizing reliable turning ON or OFF the discharge circuit.