Display Device Hybrid Current PWM Drive Circuit
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Solution Overview
Problem
Existing display devices with light-emitting elements, such as micro LEDs and OLEDs, face challenges in achieving high-speed pixel writing and fine gradation expression due to the limitations of current drive systems and pulse width modulation systems.
Innovation Solution
A display device configuration that includes a plurality of light-emitting elements, first and second pixel circuits, drive transistors, and coupling switching transistors, where the coupling switching transistors are turned off during non-emission periods to prevent unintended potential application to the light-emitting elements, allowing for efficient gradation control by combining current drive and pulse width modulation systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a current drive system is used to adjust current value for gradation expression, then gradation control is achieved, but light emission intensity may differ from desired intensity depending on transistor characteristics
Solution Approach 1:
The patent combines current drive system and pulse width modulation system into a hybrid drive system. The current drive transistor adjusts current value for gradation, while the coupling switching transistor controls light emission timing. This merging allows the system to achieve both gradation control capability and accurate light emission intensity by using PWM to compensate for transistor characteristic variations.
Solution Approach 2:
The coupling switching transistor acts as an intermediary between the current drive transistor and the light-emitting element. It receives the current-adjusted signal from the drive transistor and controls the actual light emission timing, mediating between current control and precise light output timing to achieve accurate gradation expression.
2Manufacturing precision
If pulse width modulation system is used to control lighting time for gradation, then gradation expression is achieved, but drive time is required to rise to desired current value making high-speed pixel writing difficult
Solution Approach 1:
The current drive transistor preliminarily adjusts the current value before the light emission occurs. By pre-adjusting the current through the coupling switching transistor during the writing period, the system prepares the optimal current level in advance, eliminating the need for slow current rise during light emission and enabling high-speed pixel writing.
Solution Approach 2:
The system dynamically switches between current drive mode and PWM mode. During the writing period, the coupling switching transistor is turned on to allow current adjustment. During the light emission period, it is turned off to enable precise PWM control. This dynamic operation optimizes both writing speed and gradation accuracy.
3Ease of operation
If coupling switching transistors are kept on during non-emission period, then circuit remains connected, but unintended potential may be applied to light-emitting elements causing damage
Solution Approach 1:
The coupling switching transistor operates periodically, being turned on during the writing period and turned off during the light emission period and non-emission period. This periodic switching ensures the circuit is connected only when needed for writing, protecting the light-emitting element from unintended potential while maintaining ease of operation during active periods.
Data Source
AI summary
A display device includes a plurality of light-emitting elements arrayed in a display region, a first pixel circuit and a second pixel circuit coupled to each of the light-emitting elements, a first drive transistor provided to the first pixel circuit and configured to supply a first drive current to the light-emitting element, a second drive transistor provided to the second pixel circuit and configured to supply a second drive current to the light-emitting element, a drive circuit configured to supply a video signal to the first drive transistor and the second drive transistor, a first coupling switching transistor provided between the first drive transistor and the light-emitting element, and a second coupling switching transistor provided between the second drive transistor and the light-emitting element. The first coupling switching transistor and the second coupling switching transistor are turned off in a non-emission period of the light-emitting element.