LCOS Pixel Modulation Using Local Latches for Leakage-Free Gray Scale
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Solution Overview
Problem
Existing analog and digital LCOS displays face challenges in maintaining accurate pixel voltages due to leakage and slow charging times, leading to image distortions and inefficiencies, especially in small pixel sizes, while digital displays struggle with high data rates and phase modulation limitations.
Innovation Solution
A pixel array architecture with digital circuitry under each pixel, using a waveform generator and local voltage modulation to achieve continuous voltage control, allowing for high-frequency pixel updates and reduced phase ripple, eliminating the need for bit-planes and external drivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog pixel circuitry is used with small pixel sizes, then the display can achieve continuous voltage control for gray-scale images, but the capacitors cannot hold accurate charge long enough due to leakage currents
Solution Approach 1:
The patent replaces the analog capacitor-based voltage storage mechanism with a digital latch-based storage mechanism. Each pixel uses a latch circuit that can store digital values (0 or 1) indefinitely without leakage, eliminating the charge retention problem inherent in analog capacitors. The liquid crystal layer still provides continuous voltage control through the digital-to-analog conversion at the pixel electrode, combining the best of both digital storage stability and analog modulation capability.
2Reliability
If digital pixel circuitry is used to eliminate leakage issues, then charge retention is improved, but the data rate requirements become excessively high
Solution Approach 1:
The patent segments the frame into multiple sub-frames, with each sub-frame containing a portion of the total pixel data. By dividing the data into smaller chunks that can be written in parallel across multiple pixels during each sub-frame, the system achieves high charge retention with reduced data rate requirements. The latch-based storage allows data to be written once per sub-frame and retained until the next update, eliminating the need for continuous high-rate data transmission.
3Adaptability or versatility
If bit-planes are used for digital display control, then phase modulation can be achieved, but the image updates slowly and power consumption is high
Solution Approach 1:
The patent implements dynamic pixel modulation where the pixel electrode voltage is modulated at a frequency much higher than the liquid crystal response time. This allows the system to achieve phase modulation through duty-cycle control of high-frequency pulses, enabling fast image updates. The liquid crystal layer integrates these high-frequency pulses into an effective average voltage, providing both speed and modulation capability without the slow bit-plane updates of conventional digital displays.
4Loss of time
If multiple analog data sources are used to reduce charge time, then the frame time can be reduced, but the device complexity increases significantly
Solution Approach 1:
The patent uses preliminary action by pre-charging pixel capacitors to intermediate voltage levels during sub-frames, rather than waiting for complete frame-time charging. The latch-based storage allows data to be prepared and written in advance during sub-frame intervals, reducing the actual charge time required. This eliminates the need for multiple parallel data sources while achieving fast charge times through time-division multiplexing of the single data source across multiple sub-frames.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient, high-bit-depth displays with minimal transistors per pixel, achieving fast image updates and reduced power consumption, suitable for small pixel sizes without image distortion.
Implementation Method 1
the Liquid Crystal (LC) directly above each of these pixels. As a result, they ultimately determine (for Amplitude Displays) the amount of polarization change for light reflected from that pixel, or (for Phase Displays) the amount of phase shift applied to the light reflected from that pixel
Data Source
AI summary
A system for generating a voltage at a pixel array includes a plurality of display pixels forming the pixel array, each display pixel comprising a pixel circuit for driving the pixel. The system further comprises a row formatter configured to store a plurality of bits representing image data for a row of display pixels of the LCOS array; a row controller configured to write a subset of the plurality of bits representing image data for a pixel of the row into a plurality of data latches of said pixel circuit; and a waveform generator for generating reference pulses represented by a set of reference bits. The pixel circuit is configured to compare each reference bit to corresponding bits stored in the latches of each pixel circuit, and generate voltage at an electrode of each pixel based on this comparison.