Pixel Driving Circuit Stabilizes Luminance via Capacitor Reset
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Solution Overview
Problem
Conventional pixel driving circuits face issues due to differences in internal threshold voltage and impedance, affecting luminance in micro light emitting devices, particularly under varying driving currents.
Innovation Solution
A pixel driving device comprising a capacitor, reset circuit, compensation circuit, driving transistor, and additional transistors that reset and compensate voltages to generate a driving voltage difference, allowing for a driving current independent of the power supply voltage, thereby stabilizing luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional driving circuit structure is used with micro light emitting device, then high luminance can be achieved under high driving current, but internal threshold voltage differences and impedance variations cause luminance inconsistency
Solution Approach 1:
The patent applies preliminary action by resetting the capacitor to a known reference voltage before the driving current is applied. The reset circuit pre-charges or pre-discharges the capacitor to eliminate threshold voltage differences and impedance variations before the actual driving operation, ensuring luminance consistency from the start of each frame or sub-frame.
Solution Approach 2:
The patent implements feedback by using the capacitor to store voltage information that reflects the driving current history. The capacitor voltage serves as a feedback signal that compensates for threshold voltage differences and impedance variations, allowing the circuit to self-correct and maintain consistent luminance across different pixels and time periods.
2Illumination intensity
If high driving current is applied to achieve high luminance, then brightness is improved, but power supply voltage variations due to impedance affect driving current stability
Solution Approach 1:
The patent introduces the capacitor as an intermediary element between the power supply and the micro light emitting device. The capacitor decouples the driving current from direct power supply voltage variations by storing charge and releasing it in a controlled manner, thereby stabilizing the driving current despite impedance-induced voltage fluctuations.
Solution Approach 2:
The patent changes the electrical parameters by using the capacitor to store and release voltage, effectively transforming the driving mechanism from direct voltage control to capacitor-based voltage control. This parameter change allows the circuit to maintain stable driving current by leveraging the capacitor's voltage storage capability rather than relying directly on power supply voltage.
3Ease of manufacture
If internal threshold voltage differences are present in driving transistor, then device manufacturing is simplified, but driving current varies causing luminance differences
Solution Approach 1:
The patent uses feedback through the capacitor to compensate for threshold voltage differences. The capacitor stores voltage information that reflects the threshold voltage variations of different transistors, and this stored voltage serves as a compensatory signal that equalizes the driving current across pixels with different threshold voltages, ensuring luminance uniformity without requiring precise transistor matching.
Solution Approach 2:
The patent enables self-service by allowing each pixel's capacitor to automatically compensate for its own transistor's threshold voltage difference. Each pixel independently stores and uses its own threshold voltage information in the capacitor, eliminating the need for external calibration or matching processes, thus maintaining both ease of manufacture and luminance uniformity.
Data Source
AI summary
A pixel driving device includes a capacitance, a reset circuit, a compensation circuit, a driving transistor and a first transistor. Reset circuit and compensation circuit are coupled to a first end and a second end of capacitance. First transistor is coupled between second end of driving transistor and second end of capacitance. Reset circuit resets first end of capacitance at a power supply voltage and reset second end of capacitance at a reference voltage according to a first sweep signal respectively. Compensation circuit writes a data voltage into first end of capacitance via driving transistor and second end of capacitance is maintained at reference voltage according to a second sweep signal. First transistor generates a driving voltage difference between first end and second end of capacitance according to a control signal. Driving transistor outputs a current to a luminous element according to driving voltage difference.