Liquid Crystal Display Signal Processing for Ramp Waveform Ringing
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Solution Overview
Problem
In liquid crystal display devices, when many pixels have the same gradation in the horizontal direction, large load fluctuations occur, leading to ringing in the analog ramp waveform, which deteriorates the reproducibility of gradation.
Innovation Solution
A signal processing device generates a gradation histogram to determine the number of pixels for each gradation, calculates holding periods based on gradation differences and voltage slew rates, and selects a provisional holding period to minimize ringing, adjusting the ramp waveform signal to optimize gradation display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sampling is performed by comparing gradation data with counter output within one horizontal scanning period, then the analog ramp waveform can be sampled at the timing when both coincide, but large load fluctuations occur when many pixels have the same gradation, causing ringing in the analog ramp waveform
Solution Approach 1:
The patent calculates the distribution of gradation values in advance and determines the optimal holding period for each gradation before sampling occurs. This preliminary analysis allows the system to anticipate when multiple pixels will have the same gradation and adjust the sampling timing accordingly, preventing ringing by avoiding simultaneous switching of multiple analog switches at critical moments in the ramp waveform cycle.
2Productivity
If many analog switches are turned off simultaneously at sampling timing, then sampling can be performed efficiently, but large load fluctuations occur causing ringing in the analog ramp waveform
Solution Approach 1:
The patent dynamically changes the holding period parameter for each gradation value based on its frequency distribution. By adjusting this temporal parameter, the system spreads out the switching events of analog switches over time, preventing simultaneous turn-off of multiple switches and thereby eliminating the harmful ringing effect while preserving sampling efficiency.
Data Source
AI summary
A display gradation number acquisition unit acquires the number of display gradations of the video data during each horizontal scanning period based on a gradation histogram. A first display gradation holding period value generator generates a first display gradation holding period value based on a gradation value difference. A second display gradation holding period value generator generates a second display gradation holding period value based on the number of pixels for each display gradation. A holding period provisional value generator selects a display gradation holding period value having a larger value to generate a holding period provisional value. A holding period total value generator generates a holding period total value that is a sum of the holding period provisional value during each horizontal scanning period. A holding period optimum value generator generates a holding period optimum value of each display gradation.