Amplifier Driver Circuit with Alternating Offset Voltages
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Solution Overview
Problem
Active Matrix Organic LED (AMOLED) displays face challenges in maintaining image quality due to slight variations in voltages generated by drivers, which can result in image artifacts, especially when using gamma buffered driving methods, where differences in loading between channels and buffers introduce voltage level variations.
Innovation Solution
A driver circuit that operates in alternating modes to provide opposing offset voltages, switching between non-inverting and inverting offset operations for channel and gamma amplifiers, canceling out imperfections over frame times to reduce image variation, with control signals managing these modes and stored in non-volatile memory for precise timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gamma buffered driving is used to amplify gray voltage levels, then image quality is maintained through gamma correction, but loading effects between different channels introduce voltage level variations
Solution Approach 1:
The patent divides the single large gamma buffer into multiple smaller channel buffers, one for each channel. This segmentation reduces the loading effects between channels while maintaining the necessary gamma correction functionality, as each buffer handles only its designated channel's voltage levels.
Solution Approach 2:
The patent inverts the traditional approach by having each channel have its own dedicated buffer rather than sharing a common buffer. This inversion of the buffer architecture eliminates the loading effects that occur when multiple channels share a single buffer, as each channel operates independently with its own buffer.
2Manufacturing precision
If channel buffered driving is used with dedicated buffers for each channel, then loading effects are reduced, but variations between the buffers introduce differences between voltage levels on different channels
Solution Approach 1:
The patent merges the functions of the channel buffers by having them alternately drive different channels in a time-multiplexed manner. Instead of each buffer being permanently dedicated to one channel, buffers are shared across channels through time-multiplexing, reducing variations between buffers while still providing dedicated buffering capability.
Solution Approach 2:
The patent implements periodic switching between different buffer configurations, where buffers alternately serve different channels in a regular pattern. This periodic action allows the system to average out variations between individual buffers over time, improving voltage level consistency across channels.
3Manufacturing precision
If amplifiers operate with fixed offset voltages, then simple circuit design is maintained, but image variation due to amplifier imperfections cannot be reduced
Solution Approach 1:
The patent makes the amplifier offset voltages dynamic by periodically alternating between positive and negative offsets. Instead of fixed offset voltages, the system dynamically switches the offset polarity, allowing the amplifiers to average out their imperfections over time while maintaining relatively simple circuit design.
Solution Approach 2:
The patent applies periodic switching of the amplifier offset voltages between positive and negative values. This periodic action causes the amplifier imperfections to manifest as alternating positive and negative errors that average to zero over time, reducing image variation without requiring complex compensation circuits.
Data Source
AI summary
A driver circuit can include a channel amplifier configured to operate in a first mode to provide a channel amplifier output including a positive offset voltage responsive to a first state of a control signal and configured to operate in a second mode to provide the channel amplifier output including a negative offset voltage responsive to a second state of the control signal. Related displays, apparatus, and methods are disclosed.