Output Amplifier Current Mirror Acceleration for Fast Signal Tracking
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Solution Overview
Problem
Current semiconductor devices face challenges in achieving high-speed amplification operations that accurately follow level changes in input signals, leading to display quality deterioration due to increased load capacitances and reduced driving periods in display devices like active-matrix liquid crystal displays and organic EL displays.
Innovation Solution
The semiconductor device incorporates an output circuit with a differential input stage, an output amplifier stage, and an amplification accelerator circuit that generates and manages currents to accelerate the amplification process, using multiple differential stages and current mirrors to accurately reflect voltage changes and drive transistors in the output amplifier stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the load capacitances of data lines are increased to support higher resolution displays, then the display resolution is improved, but the amplification operation cannot follow level changes of input signals quickly enough, causing output signal delay
Solution Approach 1:
The output circuit is divided into two independent amplification paths: a normal amplification circuit for accurate voltage reproduction and a peak hold circuit for capturing and holding peak input signal values. This segmentation allows each circuit to specialize in its function, with the peak hold circuit providing fast response for high-speed amplification while the normal circuit maintains accuracy.
Solution Approach 2:
A selection circuit acts as an intermediary between the normal amplification circuit and the peak hold circuit, dynamically selecting which circuit's output to provide based on the current operating conditions. This intermediary enables the system to switch between accuracy-oriented and speed-oriented modes, resolving the contradiction between amplification speed and voltage accuracy.
2Productivity
If the driving period per pixel is reduced to increase the data transmission rate, then the productivity is improved, but the amplification operation cannot complete within the shorter time, causing deterioration in image quality
Solution Approach 1:
The peak hold circuit performs preliminary action by capturing and holding the peak value of the input signal before the normal amplification circuit completes its operation. This pre-captured peak value is then used to generate the output signal, ensuring that the amplification operation completes within the reduced driving period while maintaining image quality.
Solution Approach 2:
The system dynamically adapts its amplification mechanism based on timing requirements. When the driving period is short, the peak hold circuit takes over to provide fast response. This dynamic switching between amplification modes allows the system to maintain reliability (image quality) even when productivity (data transmission rate) is increased through reduced driving periods.
3Measurement precision
If a current mirror with narrow channel width relative to channel length is used to achieve high accuracy mirror current, then the measurement precision is improved, but the response characteristic to variations in mirror current deteriorates
Solution Approach 1:
The current mirror function is segmented between two circuits: the normal amplification circuit uses a standard current mirror for high accuracy current reproduction, while the peak hold circuit uses a different configuration optimized for fast response characteristics. This segmentation allows each circuit to optimize for its primary function without compromising the other.
Solution Approach 2:
The selection circuit serves as an intermediary that directs the output from either the normal amplification circuit (with accurate current mirror) or the peak hold circuit (with fast response) based on the current operational requirements. This intermediary enables the system to achieve both high accuracy and fast response characteristics by selecting the appropriate circuit path.
Data Source
AI summary
A current corresponding to the difference between an input signal voltage and an output signal voltage is generated as an amplification acceleration current. The amplification acceleration current is sent to an output node of a current mirror, which drives a transistor in an output amplifier stage, and therefore added to a current to drive the transistor in the output amplifier stage.