CMOS Pixel Circuit Layout for High-PPI Leakage Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Display devices, particularly those used in virtual reality (VR) and augmented reality (AR), face limitations due to the narrow pitch of pixel circuits, which restricts the number of transistors and applied signals, hindering high pixel density and area efficiency.
Innovation Solution
A pixel circuit design incorporating N-type and P-type transistors forming CMOS configurations, with specific transistors diode-connecting to minimize leakage current and reduce area, while compensating for threshold voltage, thereby optimizing pixel circuit performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pitch occupied by a pixel circuit is narrowed to increase pixel density, then the PPI is improved, but the number of transistors and signals that can be applied to the pixel circuit is limited
Solution Approach 1:
The patent merges the functions of multiple transistors into a single transistor structure. Specifically, the data write transistor and first light emission control transistor are combined into a single transistor element, reducing the total number of transistors while maintaining the necessary functionality for data writing and light emission control. This merging allows the pixel circuit to achieve high PPI without being constrained by the number of available transistor elements.
2Area of stationary object
If the number of transistors is reduced to accommodate narrow pitch, then the area is reduced, but leakage current increases
Solution Approach 1:
The patent converts the harmful leakage current into a beneficial feature by utilizing the body effect. The body effect, which normally causes leakage, is harnessed to compensate for threshold voltage shifts in the transistor. By strategically designing the source and drain connections to exploit the body effect, the patent turns the leakage current phenomenon into a mechanism for maintaining stable transistor operation and compensating for threshold voltage variations, thereby reducing the need for additional compensation circuits.
3Object-generated harmful factors
If transistors are diode-connected to minimize leakage current, then the harmful factors are reduced, but the device complexity increases
Solution Approach 1:
The patent makes the compensation transistor serve multiple functions: it acts as both a compensation element for threshold voltage and as a diode-connected transistor for leakage current minimization. The same transistor element performs both compensation and leakage control, eliminating the need for separate dedicated circuits for each function. This multi-functionality reduces the overall device complexity while achieving the desired leakage current reduction.
4Measurement precision
If the pixel circuit area is reduced to increase PPI, then the display density is improved, but unnecessary light emission may occur
Solution Approach 1:
The patent applies preliminary action by using the initialization transistor to set the initial state of the pixel circuit before the data write transistor activates. The initialization transistor ensures that the holding capacitor is properly initialized and that the transistor gates are in the correct state before data writing begins. This preliminary initialization prevents unintended light emission during the data writing process by ensuring all control transistors are in the correct off-state before data is written, thereby preventing unnecessary light emission while maintaining high pixel density.
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
The design minimizes leakage current, reduces pixel circuit area, and prevents unnecessary light emission, enhancing pixel density and efficiency in display devices.
Implementation Method 1
when the compensation transistor is turned on, the compensation transistor may diode-connect the driving transistor
Implementation Method 2
a light emitting element including an anode electrode and a cathode electrode receiving a second power voltage
Data Source
AI summary
A pixel circuit includes a light emitting element including an anode electrode and a cathode electrode, a driving transistor including a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node, a data write transistor including a gate electrode, a first electrode, and a second electrode connected to the second node, a compensation transistor including a gate electrode, a first electrode connected to the third node, and a second electrode connected to the first node, an initialization transistor including a gate electrode, a first electrode, and a second electrode connected to the first node, a first light emission control transistor including a gate electrode, a first electrode, and a second electrode connected to the second node, and a storage capacitor including a first electrode and a second electrode connected to the first node.