LCD Drive Operational Amplifier for Balanced Slew Rates
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Solution Overview
Problem
Conventional operational amplifiers used in liquid crystal display devices face challenges in meeting the requirements for 2H inversion driving due to imbalanced rising and falling slew rates and limited drive current capabilities, which can result in vertical streaks and inadequate gamma amplification for both polarities.
Innovation Solution
The operational amplifier is configured with a first and second output transistor connected in series, a phase-compensating element, and a floating current source, allowing for symmetrization of rising and falling slew rates and securing drive current during 2H inversion driving through a simple circuit configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional operational amplifier configuration is used, then circuit simplicity is maintained, but rising and falling slew rates become imbalanced and drive current is insufficient
Solution Approach 1:
The patent applies asymmetry by introducing a floating current source that differentially connects to the gates of the first and second output transistors. This asymmetric current injection compensates for the inherent symmetry limitations of the push-pull output stage, enabling balanced rising and falling slew rates without requiring complex additional circuitry. The floating current source creates controlled asymmetry in gate voltages to achieve symmetric performance.
2Use of energy by moving object
If conventional operational amplifier configuration is used, then power consumption is reduced, but drive current capability becomes insufficient for 2H inversion driving
Solution Approach 1:
The patent implements dynamics by making the output stage adaptable through the floating current source. The differential connection to the gates of the output transistors allows the circuit to dynamically adjust its drive capability based on the instantaneous output voltage level. During 2H inversion driving, this dynamic adjustment ensures sufficient drive current is available when needed, while maintaining low power consumption during normal operation.
3Measurement precision
If conventional operational amplifier configuration is used, then offset voltage effects are significant, but circuit complexity increases with compensation mechanisms
Solution Approach 1:
The patent applies self-service by implementing automatic offset compensation through the floating current source mechanism. The circuit self-adjusts by differentially connecting the floating current source to the gates of the output transistors, which automatically compensates for offset voltage effects without requiring external adjustment or complex compensation circuits. The system serves itself by using the same floating current source that balances slew rates to also compensate for offset voltages.
Data Source
AI summary
The present invention enables rising and falling slew rates to be symmetrized and secures a drive current at the time of 2H inversion driving. An operational amplifier in accordance with one aspect of the present invention includes: a first output transistor and a second output transistor connected in series between a first power supply and a second power supply; an output terminal connected to a node between the first output transistor and the second output transistor; a phase-compensating element provided either between the gate of the first output transistor and the output terminal or between the gate of the second output transistor and the output terminal; and a floating current source connected between the gate of the first output transistor and the gate of the second output transistor.