Gray-Scale Voltage Circuit Stabilizing Luminance via Constant Current
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Solution Overview
Problem
Gray-scale voltage generating circuits using ladder resistor circuits face issues with luminance changes due to power supply tolerance, as the potential difference between the gate and source of the drive transistor changes, affecting the luminance of light-emitting devices in display units.
Innovation Solution
Incorporating a constant current source connected in series with the ladder resistor circuit, where the current source transistor and a voltage setting section select a voltage to determine the current flowing through the transistor, ensuring a constant potential difference and reducing luminance variations by using a constant current source and voltage setting section to manage the IR drop from the reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a ladder resistor circuit is used to generate gray-scale voltages, then the circuit structure is simple, but luminance changes occur due to power supply tolerance
Solution Approach 1:
A constant current source is introduced as an intermediary component between the power supply and the ladder resistor circuit. This constant current source maintains a stable current flow through the ladder resistors, thereby stabilizing the gray-scale voltage generation against power supply fluctuations. The constant current source acts as a mediator that isolates the ladder resistor circuit from power supply tolerance effects.
Solution Approach 2:
The invention changes the operating parameter from voltage-based control to current-based control. By using a constant current source instead of directly connecting the ladder resistor circuit to the power supply, the system maintains stable current flow even when power supply voltage varies. This parameter change from voltage to current control resolves the luminance stability issue caused by power supply tolerance.
2Manufacturing precision
If the reference voltage changes due to power supply tolerance, then the gray-scale voltage values change proportionally, but the potential difference between gate and source of drive transistor changes causing luminance variation
Solution Approach 1:
The constant current source serves as an intermediary that decouples the relationship between power supply voltage changes and gray-scale voltage changes. By maintaining constant current through the ladder resistors, it ensures that the voltage division ratios remain stable even when the reference voltage fluctuates, thereby preventing luminance variation.
Solution Approach 2:
The constant current source creates a stable electrical environment by maintaining constant current flow through the ladder resistor circuit. This stabilizes the potential distribution across the resistors, ensuring that the potential difference between gate and source of the drive transistor remains constant despite reference voltage changes, thus achieving luminance consistency.
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
This configuration maintains consistent luminance by stabilizing the potential difference between the gate and source of the drive transistor, even with power supply tolerance, and corrects variations in gray-scale voltage values caused by resistor variations, thereby reducing luminance changes and ensuring consistent display performance.
Implementation Method 1
a ladder resistor circuit including a plurality of resistors connected in series to one another, and configured to output a plurality of gray-scale voltages with different voltage values from ends of the respective resistors
Implementation Method 2
a voltage setting section configured to select one voltage from the plurality of voltages and set the selected voltage as a voltage determining a current that is to flow through the current source transistor
Data Source
AI summary
A gray-scale voltage generating circuit includes: a ladder resistor circuit including a plurality of resistors connected in series to one another, and configured to output a plurality of gray-scale voltages with different voltage values from ends of the respective resistors; and a constant current source configured to be connected in series to the ladder resistor circuit, in which the constant current source includes a current source transistor configured to be connected in series to the ladder resistor circuit, and a voltage setting section configured to select one voltage from the plurality of voltages and set the selected voltage as a voltage determining a current that is to flow through the current source transistor.