PWM Driven Pixel Circuit for Grayscale Control
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Solution Overview
Problem
Existing display devices face challenges in precisely controlling grayscale due to variations in driving transistors, leading to inconsistent brightness and image quality.
Innovation Solution
A pulse width modulation (PWM) driven pixel circuit is introduced, comprising a data latch, PWM generator, and counter, which generates PWM signals based on pixel data and scan signals to accurately control the duration of voltage or current, thereby precisely rendering grayscale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If constant voltage is continuously applied to the liquid crystal medium, then the display device can maintain simple driving, but it causes LCD image blur and deterioration of display quality
Solution Approach 1:
The patent applies periodic action by using alternating voltage polarity reversal in the liquid crystal display. The driving circuit switches the voltage polarity between positive and negative in alternating frames, preventing the constant voltage application that causes image blur while maintaining display quality. This periodic polarity reversal is implemented through the inversion drive mode where even and odd frames have opposite polarity.
2Adaptability or versatility
If driving transistors are used to control voltage or current for grayscale expression, then the display device can achieve grayscale control, but transistor threshold voltage deviations cause inconsistent grayscale and uneven brightness
Solution Approach 1:
The patent replaces the analog voltage/current control mechanism (which is sensitive to transistor variations) with a digital PWM control system. Instead of relying on precise analog voltage control that is affected by transistor threshold voltage deviations, the system uses digital pulse width modulation to control the display medium. This digital approach eliminates the impact of transistor manufacturing variations on grayscale consistency.
Solution Approach 2:
The patent changes the control parameter from continuous voltage/current magnitude to discrete PWM duty cycle. By controlling the duration of voltage application through PWM rather than the voltage magnitude itself, the system achieves grayscale expression while being immune to transistor threshold voltage variations. The PWM generator creates precise timing control that translates digital data into accurate display output.
3Measurement precision
If PWM generator and counter are added to achieve precise grayscale control, then the accuracy of grayscale control is improved, but the device complexity increases
Solution Approach 1:
The patent merges the PWM generator and counter into an integrated unit that works together as a cohesive grayscale control system. Rather than implementing separate independent components, the design combines these functions into a unified circuit module that can be efficiently integrated into the pixel circuit. This merging approach achieves precise grayscale control while minimizing the increase in overall device complexity.
Data Source
AI summary
A pixel circuit and a display device using a pulse width modulation generator are provided. The pixel circuit has a data latch; and a pulse width modulation (PWM) generator, which is electrically coupled to the data latch, a scan line and a counter; wherein, the pulse width modulation generator is based on the pixel data, the scan signal and a counter code generated by the counter to generate a pulse width modulation (PWM) signal. Therefore, the pixel signal can be generated in a voltage and/or current mode according to the PWM signal and connected to the corresponding pixel electrode of the pixel display medium module, so that the period time for driving the display medium by accurately controlling the voltage and/or current to precisely provide grayscale function of the display.