Pixel Circuit Capacitive Memory Inverter Polarity
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Solution Overview
Problem
The complexity and area occupation of static random access memory (SRAM) in pixel structures hinder microminiaturization, and dynamic random access memory (DRAM) requires frequent refresh operations, leading to higher power consumption.
Innovation Solution
A liquid crystal display device configuration using a capacitive element connected to a pixel electrode to hold signal potentials, with an inverter circuit that inverts the polarity of the held potential and sets the input potential to the middle of the operating supply voltage range, allowing for simplified pixel structure and reduced power consumption during refresh operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If SRAM is used as built-in memory in the pixel, then memory display mode can be realized, but pixel structure complexity increases and area occupation increases
Solution Approach 1:
The patent extracts the memory function from the complex SRAM structure and implements it using a simple capacitive element (holding capacitance) that retains charge between frames. This capacitive memory stores the grayscale signal potential without requiring the complex feedback loops and multiple transistors of SRAM, thereby achieving memory display mode capability while significantly reducing pixel structure complexity.
Solution Approach 2:
The patent uses a simple capacitive element that can be easily charged and discharged, replacing the more complex and expensive SRAM structure. The capacitive memory is sufficient for the display application and can be reliably reset and recharged each frame without requiring the robust but complex SRAM architecture.
2Device complexity
If DRAM is used as built-in memory in the pixel, then pixel structure is simplified, but frequent refresh operations are required leading to higher power consumption
Solution Approach 1:
The patent applies preliminary action by charging the capacitive element (holding capacitance) with the signal potential reflecting the grayscale before the refresh operation. This pre-charged state allows the memory to maintain its data without requiring continuous refresh operations, thereby reducing power consumption while keeping the pixel structure simple like DRAM.
3Device complexity
If capacitive element is used to hold signal potential, then pixel structure is simplified, but potential distribution during readout may affect operating margin
Solution Approach 1:
The patent introduces an intermediary buffer capacitance (Cbuf) during the readout operation. This buffer acts as a mediator between the holding capacitance and the inverter circuit, temporarily storing the charge during transfer. The buffer capacitance ensures complete charge transfer and stabilizes the potential at the inverter input, preventing potential distribution issues and maintaining the operating margin while keeping the overall pixel structure simplified.
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 configuration enables reduced power consumption and improved operating margins by eliminating the need for charge and discharge of high load capacitance during refresh, while maintaining proper potential relationships between pixel and counter electrodes.
Implementation Method 1
a capacitive element configured to be connected to the pixel electrode of liquid crystal capacitance and hold a signal potential reflecting a grayscale
Implementation Method 2
an inverter circuit configured to invert the polarity of a held potential read out from the capacitive element
Implementation Method 3
liquid crystal capacitance 91, holding capacitance 92, an SRAM 93, and five switching transistors 94 to 98
Data Source
AI summary
The present application provides a display device having a pixel circuit including: a pixel electrode; a capacitive element configured to be connected to the pixel electrode of liquid crystal capacitance and hold a signal potential reflecting a grayscale; and an inverter circuit configured to invert polarity of a held potential read out from the capacitive element, wherein input potential of the inverter circuit is set to middle potential in an operating supply voltage range of the inverter circuit in operation of inverting the polarity of the held potential and writing an inverted potential to the capacitive element again after reading out the held potential from the capacitive element.