LCD Ramp Signal Correction for Stable Gradation and Luminance
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Solution Overview
Problem
Existing liquid crystal display apparatuses struggle to sufficiently reduce image quality deterioration due to fluctuations in power supply voltage and in-plane luminance unevenness, despite effectively suppressing ramp voltage fluctuations.
Innovation Solution
A liquid crystal display apparatus with a ramp signal generation circuit that shifts ramp signals by different shift amounts and a signal processing circuit that adds correction values to picture signals, combined with a switch circuit to output appropriate ramp signals to pixels, thereby stabilizing power supply voltage and reducing image quality issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple analog switches simultaneously sample ramp voltage for pixels with same gradation level, then writing efficiency is improved, but load fluctuation on feeding line increases causing ramp voltage ringing
Solution Approach 1:
The patent divides the pixel array into multiple groups (e.g., even columns and odd columns) with separate feeding lines. By segmenting the load distribution across multiple independent feeding lines, simultaneous switching of analog switches in different groups does not cause cumulative load fluctuations on a single line, thereby suppressing ramp voltage ringing while maintaining high writing efficiency.
2Stability of the object's composition
If ramp voltage fluctuation is suppressed by segmented feeding lines, then ramp voltage stability is improved, but power supply voltage fluctuation remains causing image quality deterioration
Solution Approach 1:
The patent introduces a feedback mechanism where the actual ramp voltage is monitored and compared against a reference value. Correction values are calculated based on the detected deviations and fed back to adjust the ramp voltage generation, thereby compensating for power supply voltage fluctuations and preventing image quality deterioration such as luminance unevenness and gradation errors.
3Device complexity
If power supply voltage fluctuation is not suppressed, then device complexity remains low, but image quality deteriorates due to luminance unevenness and gradation errors
Solution Approach 1:
The patent introduces correction value calculation circuits and feedback control mechanisms as intermediary elements between the power supply and the ramp voltage generation. These intermediaries detect and compensate for power supply voltage fluctuations, thereby preventing image quality deterioration without requiring complete redesign of the power supply system, achieving a balance between complexity and performance.
Data Source
AI summary
A liquid crystal display apparatus includes: a ramp signal generation circuit configured to output shifted plurality of ramp signals; a signal processing circuit configured to add a correction value corresponding to a shift amount of an assigned ramp signal to each of a plurality of picture signals for the number of columns of the plurality of pixels; a horizontal shift register configured to sequentially capture the plurality of picture signals; a latch circuit configured to simultaneously output the plurality of picture signals; a gradation counter; a plurality of comparators configured to output a matching signal when each of the plurality of picture signals matches a count value of the gradation counter; and a switch circuit configured to output, to a pixel in a column corresponding to a comparator from which the matching signal is output, one of voltages of the plurality of ramp signals corresponding to the pixel.