VCOM Regulator Circuit for High Refresh Rate LCD Stability
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Solution Overview
Problem
The existing VCOM regulators in liquid crystal displays face challenges in maintaining stable common voltage under high frame rates, leading to inadequate charging/discharging and deteriorated visual experience, especially with patterns like green-magenta, due to parasitic RC loads and insufficient drive capability.
Innovation Solution
A voltage control circuit with an operational amplifier in a negative feedback configuration, including NMOS and PMOS transistors, and control signals (FOD and ROD) to enhance the drive capability by stabilizing the VCOM voltage through over-drive capabilities, effectively addressing the parasitic RC load challenges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the refresh rate is increased to meet performance requirements, then the display performance is improved, but the VCOM regulator cannot complete charging/discharging in time due to parasitic RC loads
Solution Approach 1:
The patent applies preliminary action by introducing a pre-charge circuit that performs charging before the main switching operation. The pre-charge circuit charges the parasitic capacitance of the pixel electrode in advance, ensuring that when the main switching occurs at high refresh rates, the voltage has already been partially established, allowing the VCOM regulator to complete charging/discharging within the reduced time window.
Solution Approach 2:
The patent uses an intermediary approach by inserting a pre-charge circuit between the VCOM regulator and the pixel electrode. This pre-charge circuit acts as a mediator that handles the initial charging task, reducing the burden on the main VCOM regulator during high-frequency switching operations and enabling reliable voltage delivery at higher refresh rates.
2Productivity
If the frame rate is increased to 120 Hz or 144 Hz, then the display performance is improved, but the visual experience is deteriorated due to insufficient drive capability
Solution Approach 1:
The pre-charge circuit performs preliminary charging of the pixel electrode capacitance before the main voltage switching occurs. This ensures that even at high frame rates of 120 Hz or 144 Hz, the voltage reaches the required level quickly enough to maintain proper display characteristics and prevent visual artifacts, thereby preserving visual experience while enabling higher frame rates.
3Area of stationary object
If the pixel point is farther away from the VCOM regulator, then the display coverage is improved, but the RC load is larger causing longer charging/discharging time
Solution Approach 1:
The pre-charge circuit performs charging action in advance for all pixel points, including those farther from the VCOM regulator. By initiating charging before the main switching event, the circuit ensures that even distant pixel points receive sufficient voltage within the limited time window, reducing the effective charging time loss and enabling full display coverage.
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 proposed circuit significantly improves the drive capability of the VCOM regulator, ensuring stable VCOM voltage even at high frame rates, thereby enhancing the performance and image quality of liquid crystal displays.
Implementation Method 1
an operational amplifier arranged in a negative feedback configuration
Implementation Method 2
including NMOS and PMOS transistors, and control signals (FOD and ROD) to enhance the drive capability
Data Source
AI summary
The present disclosure relates to a circuit of controlling a common voltage of a liquid crystal panel. According to an embodiment of the present disclosure, a voltage control circuit is configured to provide a common voltage to a common electrode of a liquid crystal panel. The liquid crystal panel includes M rows and N columns of pixel units. Each pixel unit is coupled to the common electrode. The voltage control circuit includes an operational amplifier arranged in a negative feedback configuration. The operational amplifier includes: an input stage, a gain stage and an output stage. The output stage includes a second NMOS transistor and a second PMOS transistor. A gate of the second NMOS transistor receives a first control signal, a drain of the second NMOS transistor is coupled to a gate of a first PMOS transistor, and a source of the second NMOS transistor is coupled to a second reference voltage. A gate of the second PMOS transistor receives a second control signal, a drain of the second PMOS transistor is coupled to a gate of a first NMOS transistor, and a source of the second PMOS transistor is coupled to a third reference voltage.