Display Driving Circuit With Capacitive Gate Hold for PWM Grayscale
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Solution Overview
Problem
Current display technologies face issues with increased power consumption and decreased grayscale control accuracy due to the need for multiple transistors in the driving current path, leading to voltage requirements that are higher than necessary and prolonged transition times in pulse width modulation, resulting in current waveform distortion and inefficiencies.
Innovation Solution
A driving circuit design incorporating a driving transistor, capacitors, and switching transistors to control the driving current, which includes a second capacitor to maintain gate voltage during emission periods, reducing the number of transistors in the current path and minimizing voltage differences, thereby reducing power consumption and improving grayscale control accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple transistors are configured on the current path of the driving current to control pulse width and amplitude, then grayscale dimming by pulse width modulation can be implemented, but the driving voltage required by the pixel circuit increases, resulting in increased power consumption
Solution Approach 1:
The patent extracts the voltage holding function from the transistor network and assigns it to a dedicated capacitor connected to the gate terminal. This separation allows the transistors to focus solely on current control while the capacitor maintains the gate voltage, reducing the voltage headroom requirement and thus power consumption.
Solution Approach 2:
The capacitor acts as an intermediary element between the control signal and the driving transistor gate. It stores the gate voltage during the emission period, enabling the transistor to maintain saturation operation without requiring continuous high voltage drive, thereby reducing overall power consumption while preserving PWM grayscale control.
2Adaptability or versatility
If multiple transistors are configured on the current path to control driving current, then pulse width modulation can be achieved, but the number of transistors increases device complexity
Solution Approach 1:
The patent extracts the timing control function from the transistor network and implements it using a capacitor-discharge mechanism. This reduces the number of transistors needed in the current path while maintaining PWM capability, as the capacitor naturally discharges to provide the timing reference for pulse width control.
Solution Approach 2:
The capacitor serves itself by automatically discharging during the emission period, providing an intrinsic timing mechanism for pulse width modulation. This self-service timing function eliminates the need for additional active control transistors, simplifying the device structure while preserving grayscale control capability.
3Measurement precision
If the transition time of the driving current is too long during pulse width modulation, then grayscale control accuracy decreases due to current waveform distortion, but reducing transition time requires faster switching that increases power consumption
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to the appropriate gate voltage level before the emission period begins. This ensures that when the transistor switches on, the gate is already at the optimal voltage for fast saturation, enabling rapid current rise without excessive power consumption during the transition.
Solution Approach 2:
The patent changes the gate voltage parameter dynamically by using the capacitor to maintain a elevated gate voltage level during the emission period. This parameter change allows the transistor to operate in deep saturation with minimal on-resistance, enabling fast current transitions with reduced power loss compared to continuous high-voltage operation.
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 driving circuit reduces power consumption and enhances grayscale control accuracy by maintaining gate voltage through capacitive coupling, ensuring efficient operation of light emitting elements with improved luminous efficiency.
Implementation Method 1
maintaining gate voltage through capacitive coupling
Data Source
AI summary
A driving circuit includes a driving transistor, first to third capacitors and first to second switching transistors. The driving transistor is electrically connected between a first driving voltage terminal and a second driving voltage terminal, configured to control a driving current flowing through a light emitting element. The first switching transistor and the first capacitor are connected in series between a first terminal and a gate terminal of the driving transistor. A first terminal of the second capacitor is electrically connected to a gate terminal of the first switching transistor. The second switching transistor is electrically connected between a second terminal of the second capacitor and a first reference voltage terminal. The third capacitor is electrically connected between a gate terminal of the second switch transistor and a sweep signal line.