Driving Circuit for Display Device Using Single Reference Current Source
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Solution Overview
Problem
Conventional current-controlled driving circuits for organic EL displays require multiple reference current sources and complex circuitry, leading to increased power consumption, larger circuit size, and reliability issues due to the inability to simultaneously store current in 1-bit DCCs, which results in luminance variations and reduced productivity.
Innovation Solution
A driving method and circuit that uses a single n-bit DCC per data line, allowing for successive writing and refreshing of image data signals within one frame period by incorporating a non-display signal scan period and resetting the current value during a blanking scan, thereby reducing circuit complexity and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple reference current sources are used in conventional driving circuits, then current storage capability is improved, but power consumption increases and circuit size enlarges
Solution Approach 1:
The patent merges multiple reference current sources into a single shared reference current source that serves all 1-bit DCCs. This is achieved by implementing a common reference current line that distributes the reference current to multiple DCC circuits, eliminating the need for separate reference current sources for each DCC while maintaining reliable current storage capability across all data lines.
Solution Approach 2:
The single reference current source is designed to serve multiple functions simultaneously - it provides reference current to all 1-bit DCCs across different data lines and supports both reading and writing operations. The reference current line acts as a universal resource that can be selectively accessed by different DCC circuits at different time periods within one frame cycle.
2Reliability
If multiple reference current sources are used, then current storage is enabled, but circuit complexity increases
Solution Approach 1:
The patent combines multiple separate reference current source circuits into a single unified reference current generation unit. This unified source connects to all 1-bit DCCs through a shared reference current line, significantly reducing the total number of circuit components and interconnections while preserving the ability to store current in each DCC independently.
Solution Approach 2:
The patent extracts the reference current generation function from individual DCC circuits and consolidates it into a separate, shared reference current source module. This separation allows the reference current functionality to be implemented once and reused by multiple DCCs, simplifying the overall circuit architecture and reducing redundancy.
3Reliability
If conventional driving circuits are used, then display function is achieved, but productivity decreases due to inability to simultaneously store current
Solution Approach 1:
The patent implements a periodic time-division multiplexing scheme where one frame period is divided into distinct reading periods and writing periods. During reading periods, data is read from pixel circuits; during writing periods, data is written to pixel circuits. This periodic alternation allows the single reference current source to sequentially serve multiple DCCs without conflict, enabling simultaneous current storage capability across the display while maintaining display functionality.
Solution Approach 2:
The patent incorporates a blanking period at the beginning of each frame where writing operations are performed before the display refreshes. This preliminary writing action ensures that all DCCs have stored their respective current values before the display period begins, allowing the system to maintain both display continuity and current storage capability without requiring multiple reference current sources.
4Area of stationary object
If circuit size is reduced for miniaturization, then display size can be increased, but defect probability increases
Solution Approach 1:
By merging multiple reference current sources into a single shared source, the patent reduces the total circuit area occupied by reference current generation components. This area reduction can be reallocated to increase the display area or improve pixel density. The shared reference current line architecture maintains reliability by providing stable current to all DCCs through a unified, well-controlled distribution network.
Solution Approach 2:
The patent changes the temporal parameters of current delivery by implementing time-division multiplexing. Instead of requiring simultaneous current availability from multiple sources, the system provides current sequentially at different time slots within each frame period. This parameter change from spatial parallelism to temporal sequentiality reduces circuit complexity and area while maintaining the functional capability of supporting multiple data lines.
Data Source
AI summary
A driving circuit of display device includes digital/current converting (DCC) circuits one for each data line. The DCC circuit operates to charge a capacitor with a reference current according to a supplied signal from a shift register. The DCC circuit stores a current value of the reference current and outputs it to a data line via a switching element that has been turned on by a digital image data signal (H) of a single line supplied from a line latch. The output value of each DCC circuit is reset one after another in every select scan period in which an OFF signal is sent to all the data lines. In this way, the reset of the output value and the output of the image data signal can be successively carried out within one frame period, enabling the data to be applied to the pixel circuit with the DCC circuits provided one for each data line. This simplifies the driving circuit that drives the pixel circuits provided with an electro-optic element and disposed in a matrix.