Pixel Circuit Stabilizing Transistor Bias for Display Quality
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Solution Overview
Problem
Display devices face issues with display quality deterioration due to changes in the hysteresis characteristic of driving transistors when driven at various frame frequencies, leading to problems like flicker and image retention.
Innovation Solution
A pixel design that includes multiple transistors and power sources with controlled voltage levels across different scan periods to stabilize the bias state of the driving transistor, preventing hysteresis characteristic shifts and maintaining consistent luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the display device is driven at various frame frequencies to achieve image display in various conditions, then adaptability is improved, but display quality deteriorates due to hysteresis characteristic changes
Solution Approach 1:
The pixel circuit applies a bias voltage to the driving transistor during a bias period before the actual display period. This preliminary action stabilizes the transistor's threshold voltage and prevents hysteresis effects that would otherwise occur when switching between different frame frequencies, thereby maintaining display quality across various operating conditions
Solution Approach 2:
The circuit changes the voltage level of the first power source depending on the operating period. During the bias period, a bias voltage is applied to the driving transistor, while during the display period, the normal driving voltage is used. This parameter change adapts the transistor's electrical characteristics to prevent hysteresis and maintain consistent display quality across different frame frequencies
2Use of energy by moving object
If the driving frequency is lowered to reduce power consumption, then energy efficiency is improved, but display quality deteriorates due to hysteresis effects
Solution Approach 1:
Before the display period at low frame frequency, the circuit performs a bias period where a bias voltage is applied to the driving transistor. This preliminary stabilization prevents hysteresis effects that would otherwise cause display quality deterioration, allowing the device to operate at low power consumption without sacrificing image quality
Solution Approach 2:
The circuit operates in periodic cycles consisting of a bias period followed by a display period. During the bias period, the driving transistor is prepared with a bias voltage to stabilize its characteristics. This periodic preparation allows the display device to maintain quality even when running at reduced frame frequencies for power savings
Data Source
AI summary
A display device includes: a pixel including a first transistor connected between a first node and a second node to generate a driving current; an emission driver supplying an emission control signal; a scan driver supplying first to fourth scan signals in a period in which the emission control signal is supplied; a data drive supplying a data signal; a power supply supplying a voltage of a first power source; and a timing controller controlling driving of the scan driver, the emission driver, the data driver, and the power supply The first scan signal controls a timing at which the voltage of the first power source is supplied to the first node or the second node. The power supply changes a level of the voltage of the first power source in one frame period.