Display Driver Calibration for Op-Amp Offset Compensation
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Solution Overview
Problem
Operational amplifiers in drive circuits for liquid crystal on silicon spatial light modulators experience random offset voltages, reducing the precision of grey-level voltage settings and affecting image quality, particularly in phase-only holographic systems where voltage errors manifest as random noise.
Innovation Solution
A method is introduced to individually compensate for the voltage offset of each operational amplifier by calibrating its parameters using a digital-to-analog converter (DAC)/operational amplifier (op-amp) pair, where each DAC/op-amp pair is uniquely dedicated to providing a specific grey-level voltage, and a calibration system adjusts the feedback parameter to minimize voltage errors, ensuring precise voltage control for each pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If operational amplifiers are used in drive circuits for grey-level voltage generation, then the circuit can provide multiple grey-level voltages, but random offset voltages in the operational amplifiers reduce the precision of voltage settings
Solution Approach 1:
The patent applies preliminary action by measuring and storing the offset voltage of each operational amplifier in advance during a test mode before normal operation. The measured offset values are saved in a lookup table, allowing the system to pre-compensate for these deviations during actual grey-level voltage generation, thereby maintaining precision while preserving versatility
Solution Approach 2:
The patent implements feedback by measuring the actual output voltage of each operational amplifier and comparing it with the expected voltage. The difference (offset) is then used to adjust subsequent voltage generation through compensation calculations, creating a closed-loop system that maintains precision despite component variations
2Measurement precision
If offset voltage compensation is implemented for each operational amplifier, then voltage precision is improved, but the device complexity increases due to additional calibration requirements
Solution Approach 1:
The calibration process is performed in advance during manufacturing or initial setup, measuring and storing offset values in a lookup table before the device enters normal operation. This preliminary action transfers the complexity from ongoing operation to one-time setup, maintaining precision without adding operational complexity
Solution Approach 2:
The patent uses a lookup table that stores pre-measured offset values for each operational amplifier. Instead of performing complex real-time calculations or measurements, the system simply retrieves the appropriate compensation value from the lookup table based on the operational amplifier being used, simplifying the compensation mechanism while maintaining precision
3Measurement precision
If each DAC/op-amp pair is uniquely dedicated to a specific grey-level voltage, then voltage control precision is improved, but the quantity of components increases
Solution Approach 1:
The patent segments the grey-level voltage generation into multiple independent DAC/op-amp pairs, with each pair dedicated to a specific grey-level voltage. This segmentation allows each component to be individually calibrated and compensated, improving precision while organizing the increased component quantity into a manageable, systematic structure
Data Source
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AI summary
A method of operating a display device comprising a drive circuit is disclosed. The drive circuit comprises a plurality of single grey-level channels, each comprising an input (412, 422), an output (418, 428) and a signal processor connected between the input and output. Each signal processor comprises a digital-to-analog converter (414, 424) and an operational amplifier (416, 426) having a voltage offset. The method comprises: converting a digital signal received at the input (412, 422) into an analog voltage (410, 420) at the output (418, 428) using each respective signal processor; switching between the analog voltage (410, 420) of each single grey-level channel using a switching circuit (430); receiving and analysing the analog voltages (410, 420) in a calibration subsystem (440), and individually compensating for the voltage offset of each op-amp (416, 426) based on the received analog voltage (410, 420) for that grey-level channel using the calibration subsystem (440).