Display Data Driver Output Amplifier for Large Capacitive Loads
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Solution Overview
Problem
The increasing load capacitance and high definition requirements in liquid crystal display devices lead to insufficient drive speed and increased power consumption in existing output amplifier circuits, particularly due to the ON resistance of output switches and the limitations of offset cancelling amplifiers in driving large load capacitances.
Innovation Solution
An output amplifier circuit with a differential stage, first and second output stages, and a control circuit that switches between connection modes to optimize the flow of voltage and reduce the impact of ON resistance, allowing for high accuracy and reduced power consumption by using a second output stage to drive the load without being affected by the ON resistance of the output switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional output amplifier circuit is used to drive large load capacitance, then the drive speed becomes insufficient and power consumption increases
Solution Approach 1:
The output amplifier circuit is divided into two separate output stages: a first output stage that operates independently and a second output stage that is activated only when needed. This segmentation allows the circuit to reduce power consumption by keeping the first stage active while the second stage remains inactive during normal operation, and only activates the second stage when additional drive capability is required for large load capacitance, thus resolving the contradiction between drive speed and power consumption.
2Speed
If the output switch ON resistance is reduced to improve drive speed, then the circuit complexity and area increase
Solution Approach 1:
The second output stage acts as an intermediary that provides additional drive current only when necessary. Instead of continuously reducing the ON resistance of the main output switch (which would increase circuit complexity), the patent introduces a secondary output stage that assists the main stage during high-current requirements. This intermediary approach achieves improved drive speed without permanently increasing circuit complexity.
3Measurement precision
If offset cancelling amplifier is used to maintain high accuracy voltage output, then the drive capability for large load capacitance is insufficient
Solution Approach 1:
The patent merges the offset cancelling functionality with the output drive capability by integrating both functions into a unified circuit architecture. The first output stage provides the primary voltage output with offset cancellation, while the second output stage is merged in parallel to provide additional drive current for large load capacitance. This combining approach maintains high voltage output accuracy while significantly improving the drive capability for large loads.
Data Source
AI summary
An output amplifier includes a differential stage having a reference voltage supplied to a first input, a first output stage that receives an output of the differential stage, a second output stage whose output is connected to a load, a capacitor element having a first end connected to a second input of the differential stage, and connection control circuits that control switching of first and second connection modes. In the first connection mode, there are provided a non-conductive state between output of the differential stage and input of the second output stage, a non-conductive state between output of the first output stage and output of the second output stage, a conductive state between output of the first output stage and the second input of the differential stage, and voltage of a second end of the capacitor element is an input voltage from the input terminal. In the second connection mode, there are provided a conductive state between output of the differential stage and input of the second output stage, a conductive state between output of the first output stage and output of the second output stage; a non-conductive state between output of the first output stage and the second input of the differential stage, a non-conductive state of the second end of the capacitor element from the input terminal, and a conductive state between the output of the first output stage and the second end of the capacitor element.