LCD Source Driver Circuit Using Shared Bias Current for Slew Rate Control
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Solution Overview
Problem
Conventional liquid crystal display (LCD) driving circuits require a large number of operational amplifiers and current sources, leading to increased chip dimensions and costs, particularly in applications with high pixel counts like 800x600 resolution.
Innovation Solution
A liquid crystal display apparatus with a panel driving device that includes a timing control circuit, a gate driving circuit, and a source driving circuit featuring operational amplifiers with differential amplifier stages and controllable current sources, utilizing a bias voltage generating unit in a current mirror configuration to adjust bias currents and slew rates based on latch pulse signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a current source is added to each operational amplifier to boost voltage slew rate, then the voltage slew rate is improved, but chip dimensions and manufacturing cost increase
Solution Approach 1:
The patent merges the current sources by using a single shared current source that serves multiple operational amplifiers simultaneously. The current source is controlled to provide bias current to selected operational amplifiers based on latch pulse signals, eliminating the need for separate current sources in each operational amplifier while maintaining the voltage slew rate enhancement function.
Solution Approach 2:
The shared current source is designed to serve multiple operational amplifiers, making it a universal component that performs the voltage slew rate boosting function for any operational amplifier that requires it. The control mechanism allows the same current source to be dynamically allocated to different operational amplifiers based on system needs.
2Speed
If a current source is added to each operational amplifier to boost voltage slew rate, then the voltage slew rate is improved, but manufacturing cost increases
Solution Approach 1:
The patent merges the current sources by using a single shared current source that serves multiple operational amplifiers simultaneously. The current source is controlled to provide bias current to selected operational amplifiers based on latch pulse signals, eliminating the need for separate current sources in each operational amplifier while maintaining the voltage slew rate enhancement function.
Solution Approach 2:
Instead of implementing physical current sources in each operational amplifier, the patent uses a single physical current source that is logically replicated or shared across multiple operational amplifiers through control signals. This approach reduces the actual hardware count while maintaining the functional capability.
3Adaptability or versatility
If the number of operational amplifiers is increased to match pixel count, then display resolution capability is improved, but device complexity increases
Solution Approach 1:
The patent merges the current sources by using a single shared current source that serves multiple operational amplifiers simultaneously. The current source is controlled to provide bias current to selected operational amplifiers based on latch pulse signals, eliminating the need for separate current sources in each operational amplifier while maintaining the voltage slew rate enhancement function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces chip dimensions and manufacturing costs by optimizing the slew rate of output voltages, achieving higher efficiency without the need for additional current sources in each operational amplifier, while maintaining stable output voltages and increased slew rates when the input bias current is at high logic levels.
Implementation Method 1
a bias voltage generating unit connected electrically to the timing control circuit for receiving the latch pulse signal therefrom, and to the operational amplifier of each of the data voltage generating units in a current mirror configuration for generating an input bias current and controlling the current source of the operational amplifier to generate the bias current
Data Source
AI summary
A liquid crystal display (LCD) apparatus includes: multiple differential amplifier stages each of which is operable to generate, according to a bias current and an input voltage, an output voltage having a magnitude and a slew rate that correspond respectively to the input voltage and a magnitude of the bias current, and serving as a data voltage of a corresponding pixel unit of an LCD panel; multiple current sources controllable to generate and provide a plurality of the bias currents to the differential amplifier stages, respectively; and a bias voltage generating unit connected electrically to the current sources in a current mirror configuration for generating an input bias current and controlling the current sources to generate the bias currents according to a latch pulse signal. The slew rate of the output voltage corresponds to a logic state of the input bias current.