Amplifier Output Voltage Swing Extender Circuit for LCD Panels
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Solution Overview
Problem
Amplifiers used in applications like LCD panels face limitations in output voltage swing due to asymmetrical supply voltages, particularly in single-supply systems, leading to incomplete charging of pixels and visible 'banding' issues when display content requires large charge amounts.
Innovation Solution
A differential amplifier circuit with a level shifting circuit, including a voltage divider and capacitance, is used to center the bias point and extend the peak-to-peak symmetric range, allowing for increased negative voltage excursion and improved charge delivery to LCD panels without a negative supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single supply voltage is used to power the amplifier, then the device complexity is reduced and ease of manufacture is improved, but the output voltage swing is limited and cannot drive the load symmetrically
Solution Approach 1:
The patent applies asymmetry by introducing a level shifting circuit that deliberately creates an asymmetric voltage offset. The circuit uses a voltage divider network (R3, R4) and capacitor (C1) to shift the amplifier's output voltage by a fixed amount, allowing the output to swing symmetrically around the load's bias point even though the amplifier itself operates from a single supply. This resolves the contradiction by accepting asymmetric internal circuitry to achieve symmetric external performance.
2Speed
If the amplifier output is centered at the supply midpoint, then the positive voltage swing is maximized, but the negative voltage swing is insufficient to restore pixel charge rapidly
Solution Approach 1:
The level shifting circuit acts as an intermediary between the amplifier output and the load input. It translates the amplifier's voltage swings into a different voltage range that is centered on the load's bias point. The voltage divider network and capacitor combine to provide this translation, enabling the output to deliver both positive and negative swings relative to the load bias, thereby increasing charge restoration speed while maintaining adequate voltage swing range.
3Stability of the object's composition
If feedback is taken directly from the amplifier output, then the control loop is simple, but the output cannot achieve the desired voltage excursion relative to the load bias point
Solution Approach 1:
The patent merges the level shifting function with the feedback network by taking the feedback signal from the same node (node 114) where the load connection occurs. This combines the voltage translation and feedback sampling functions at a single point, ensuring that the feedback signal accurately represents the load's actual voltage while maintaining a relatively simple overall circuit structure. The feedback network thus serves dual purposes: monitoring output voltage and providing the reference for the level shifting operation.
Data Source
AI summary
An amplifier output voltage swing extender circuit comprises a differential amplifier powered between first and second power supply rails, which receives first and second input signals at non-inverting and inverting inputs, respectively, and provides an output at a first output node. A level shifting circuit, preferably a voltage divider, is connected in series with the first output node and shifts the node voltage toward the second rail by a fixed amount; the shifted voltage is provided at a second output node. A feedback network couples the second output node voltage to the amplifier's inverting input, such that when a voltage VSET is applied to the non-inverting input, the maximum negative voltage excursion at the first and second output nodes is greater than the value of the VSET voltage with respect to the second supply rail.